Architecture and interconnect scheme for programmable logic circuits

Abstract: An FPGA is comprised of a number of cells which perform logical functions on input signals. Programmable intraconnections provide connectability between each output of a cell belonging to a logical cluster to at least one input of each of the other cells belonging to that logical cluster. A set of programmable block connectors are used to provide connectability between logical clusters of cells and accessibility to the hierarchical routing network. A uniformly distributed first layer of routing network lines is sued to provide connections amongst sets of block connectors. A uniformly distributed second layer of routing network lines is implemented to provide connectability between different first layers of routing network lines. Switching networks are used to provide connectability between the block connectors and routing network lines corresponding to the first layer. Other switching networks provide connectability between the routing network lines corresponding to the first layer to routing network lines corresponding to the second layer. Additional uniformly distributed layers of routing network lines are implemented to provide connectability between different prior layers of routing network lines.

Description: FIELD OF THE INVENTION The present invention pertains to the field of programmable logic circuits. More particularly, the present invention relates to an architecture and interconnect scheme for programmable logic circuits. BACKGROUND OF THE INVENTION When integrated circuits (ICs) were first introduced, they were extremely expensive and were limited in their functionality. Rapid strides in semiconductor technology have vastly reduced the cost while simultaneously increased the performance of IC chips. However, the design, layout, and fabrication process for a dedicated, custom built IC remains quite costly. This is especially true for those instances where only a small quantity of a custom designed IC is to be manufactured. Moreover, the turn-around time (i.e., the time from initial design to a finished product) can frequently be quite lengthy, especially for complex circuit designs. For electronic and computer products, it is critical to be the first to market. Furthermore, for custom ICs, it is rather difficult to effect changes to the initial design. It takes time, effort, and money to make any necessary changes. In view of the shortcomings associated with custom IC's, field programmable gate arrays (FPGAs) offer an attractive solution in many instances. Basically, FPGAs are standard, high-density, off-the-shelf ICs which can be programmed by the user to a desired configuration. Circuit designers first define the desired logic functions, and the FPGA is programmed to process the input signals accordingly. Thereby, FPGA implementations can be designed, verified, and revised in a quick and efficient manner. Depending on the logic density requirements and production volumes, FPGAs are superior alternatives in terms of cost and time-to-market. A typical FPGA essentially consists of an outer ring of I/O blocks surrounding an interior matrix of configurable logic blocks. The I/O blocks residing on the periphery of an FPGA are user programmable, such that each block can be programmed independently to be an input or an output and can also be tri-statable. Each logic block typically contains programmable combinatorial logic and storage registers. The combinatorial logic is used to perform boolean functions on its input variables. Often, the registers are loaded directly from a logic block input, or they can be loaded from the combinatorial logic. Interconnect resources occupy the channels between the rows and columns of the matrix of logic blocks and also between the logic blocks and the I/O blocks. These interconnect resources provide the flexibility to control the interconnection between two designated points on the chip. Usually, a metal network of lines run horizontally and vertically in the rows and columns between the logic blocks. Programmable switches connect the inputs and outputs of the logic blocks and I/O blocks to these metal lines. Crosspoint switches and interchanges at the intersections of rows and columns are used to switch signals from one line to another. Often, long lines are used to run the entire length and/or breadth of the chip. The functions of the I/O blocks, logic blocks, and their respective interconnections are all programmable. Typically, these functions are controlled by a configuration program stored in an on-chip memory. The configuration program is loaded automatically from an external memory upon power-up, on command, or programmed by a microprocessor as part of system initialization. The concept of FPGA was summarized in the sixty's by Minnick who described the concept of cell and cellular array as reconfigurable devices in the following documents: Minnick, R.C. and Short, R.A., "Cellular Linear-Input Logic, Final Report," SRI Project 4122. Contract AF 19(628)-498. Stanford Research Institute, Menlo Park, California, AFCRL 64-6, DDC No. AD 433802 (February 1964); Minnick, R.C., "Cobweb Cellular Arrays," Proceedings AFIPS 1965 Fall Joint Computer Conference, Vol. 27, Part 1 pp. 327-341 (1965); Minnick, R.C. et al., "Cellular Logic, Final Report," SRI Project 5087, Contract AF 19(628)-4233, Stanford Research Institute, Menlo Park, California, AFCRL 66-613, (April 1966); and Minnick, R.C., "A Survey of Microcellular Research," Journal of the Association for Computing Machinery, Vol. 14, No. 2, pp. 203-241 (April 1967). In addition to memory based (e.g., RAM-based, fuse-based, or antifuse-based) means of enabling interconnects between devices, Minnick also discussed both direct connections between neighboring cells and use of busing as another routing technique. The article by Spandorfer, L. M., "Synthesis of Logic Function on an Array of Integrated Circuits," Stanford Research Institute, Menlo Park, Calif., Contract AF 19(628)2907, AFCRL 64-6, DDC No. AD 433802 (November 1965), discussed the use of complementary MOS bi-directional passgate as a means of switching between two interconnect lines that can be programmed through memory means and adjacent neighboring cell interconnections. In Wahlstrom, S. E., "Programmable Logic Arrays - Cheaper by the Millions," Electronics, Vol. 40, No. 25. 11. pp. 90-95 (December 1967), a RAM-based, reconfigurable logic array of a two-dimensional array of identical cells with both direct connections between adjacent cells and a network of data buses is described. Shoup, R. G., "Programmable Cellular Logic Arrays," Ph.D. dissertation, Carnegie-Mellon University, Pittsburgh, PA (March 1970), discussed programmable cellular logic arrays and reiterates many of the same concepts and terminology of Minnick and recapitulates the array of Wahlstrom. In Shoup's thesis, the concept of neighbor connections extends from the simple 2-input 1-output nearest-neighbor connections to the 8-neighbor 2-way connections. Shoup further described use of bus as part of the interconnection structure to improve the power and flexibility of an array. Buses can be used to route signals over distances too long, or in inconvenient directions, for ordinary neighbor connections. This is particularly useful in passing inputs and outputs from outside the array to interior cells. U.S. 4.020,469 discussed a programmable logic array that can program, test, and repair itself. U.S. 4,870,302 introduced a coarse grain architecture without use of neighbor direct interconnections where all the programmed connections are through the use of three different sets of buses in a channeled architecture. The coarse grain cell (called a Configurable Logical block or CLB) contains both RAM-based logic table look up combinational logic and flip flops inside the CLB where a user defined logic must be mapped into the functions available inside the CLB. U.S. 4,935,734 introduced a simple logic function cell defined as a NAND, NOR or similar types of simple logic function inside each cell. The interconnection scheme is through direct neighbor and directional bus connections. US 4,700,187 and US 4,918,440 defined a more complex logic function cell where an Exclusive OR and AND functions and a register bit is available and selectable within the cell. The preferred connection scheme is through direct neighbor connections. Use of bi-direction buses as connections were also included. US 5 296 759 discloses a configurable logic array in which the interconnection routing busses are all of a standard span. Current FPGA technology has a few shortcomings. These problems are embodied by the low level of circuit utilization given the vast number of transistors available on chip provided by the manufacturers. Circuit utilization is influenced by three factors. The first one at the transistor or fine grain cell level is the function and flexibility of the basic logic element that can be readily used by the users. The second one is the ease in which to form meaningful macro logic functions using the first logic elements with minimum waste of circuit area. The last factor is the interconnections of those macro logic functions to implement chip level design efficiently. The fine grained cell architectures such as those described above, provided easily usable and flexible logical functions for designers at the base logic element level. However, for dense and complex macro functions and chip level routing, the interconnection resources required to connect a large number of signals from output of a cell to the input(s) of other cells can be quickly exhausted, and adding these resources can be very expensive in terms of silicon area. As a consequence, in fine grained architecture design, most of the cells are either left unused due to inaccessibility, or the cells are used as interconnect wires instead of logic. This adds greatly to routing delays in addition to low logic utilization, or excessive amount of routing resources are added, greatly increasing the circuit size. The coarse grain architecture coupled with extensive routing buses allows significant improvements for signals connecting outputs of a CLB to inputs of other CLBs. The utilization at the CLB interconnect level is high. However, the difficulty is the partitioning and mapping of complex logic functions so as to exactly fit into the CLBs. If a part of logic inside the CLB is left unused, then the utilization (effective number of gates per unit area used) inside the CLB can be low. Another problem with prior art FPGAs is due to the fact that typically a fixed number of inputs and a fixed number of outputs are provided for each logic block. If, by happenstance, all the outputs of a particular logic block is used up, then the rest of that logic block becomes useless. Therefore, there is a need in prior art FPGAs for a new architecture that will maximize the utilization of an FPGA while minimizing any impact on the die size. The new architecture should provide flexibility in the lowest logic element level in terms of functionality and flexibility of use by users, high density per unit area functionality at the macro level where users can readily form complex logic functions with the base logic elements, and finally high percentage of interconnectability with a hierarchical, uniformly distributed routing network for signals connecting macros and base logic elements at the chip level. Furthermore, the new architecture should provide users with the flexibility of having the number of inputs and outputs for individual logical block be selectable and programmable, and a scalable architecture to accommodate a range of FPGA sizes. SUMMARY OF THE INTENTION The present invention relates to an architecture of logic and connection scheme for programmable logic circuits, such as those for field programmable gate arrays (FPGAs), as defined in the appended claims. According to the present invention there is provided a programmable logic circuit comprising a plurality of configurable cells configured to perform logic functions on logic signals; a first set of routing lines selectively coupling the configurable cells of a logic block wherein said first set of routing lines selectively coupled to the input ports and output ports of the configurable cells of said logic block through a first set of switches; a second set of routing lines, said second set of routing lines have different spans than said first set of routing lines; a first routing line and a second routing line of said second set of routing lines, offset from each other by at least one logic block, wherein said first routing line selectively coupled to at least one routing line of a first set of routing lines of a second logic block through a second set of switches, said second logic block located adjacent to said first logic block, said first routing line spans at least the lengths of said first and said second logic blocks, and said second routing lien selectively coupled to at least one routing line of the first set of routing lines of said second logic block and at least one routing line of the first set of routine lines of a third logic block through said second set of switches, said third logic block located adjacent to said second logic block, said second routing line spans at least the lengths of said second and said third logic blocks. Also, according to the present invention there is provided a method for programming a programmable logic circuit comprising: a first set of routing lines selectively coupling configurable cells of a logic block of a plurality of logic blocks wherein said first set of routing lines selectively coupled to the input ports and output ports of the configurable cells of said logic block; a second set of routing lines, said second set of routing lines have different spans than said first set of routing lines; selectively coupling a first routing line of the second set of routing lines to at least one routing line of a first set of routing lines of a first logic block and at least one routing line of a first set of routing lines of a second logic block, said second logic block located adjacent to said first logic block, said first outing line spans at least the lengths of said first and said second logic blocks; and selectively coupling said second routing line to at least one routing line of the first set of routing lines of said second logic block and at least one routing line of the first set of routing lines of a third logic block, said third logic block located adjacent to said second logic block, said second routing line spans at least the lengths of said second and said third logic blocks. BRIEF DESCRIPTION OF THE DRAWINGS The present invention is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which like reference numerals refer to similar elements and in which: Figure 1 is a block diagram of a field programmable gate array logic upon which the present invention may be practiced. Figure 2A shows one example of an individual cell. Figure 2B shows another example of an individual cell. Figure 3A shows a logical cluster. Figure 3B shows the extension of I-matrix intraconnections of a logical cluster to a neighboring logical cluster. Figure 4A shows an example of a logical cluster with vertical block connectors. Figure 4B shows an example of a logical cluster with horizontal block connectors. Figure 5A shows the eight block connector to level 1 MLA exchange networks associated with a logical block and level 1 MLA turn points. Figure 5B shows a level 1 MLA turn point. Figure 5C shows an exchange network. Figure 6 shows the routing network for a block cluster. Figure 7A shows the block diagram of a block sector. Figure 7B shows a level 1 to level 2 MLA routing exchange network. Figure 8A shows a sector cluster. Figure 8B shows a level 2 to level 3 MLA routing exchange network. Figure 9 shows one embodiment of a hierarchical multiple level routing network for providing routability between the logical blocks and the MLA levels. Figure 10 shows another embodiment of a hierarchical multiple level routing network for providing routability between the logical blocks and the MLA levels. Figure 11 shows a block diagram of one embodiment of the hierarchical routing network wherein two groups of block connectors access the same MLA lines. Figure 12 shows a block diagram of part of the multiple level routing network which encompasses Block Connectors to the MLA-3 Level with MLA Tabs for higher levels of routing network. Figure 13 shows an MLA-1 turn network. Figure 14 shows an MLA-2 turn network. Figure 15 shows an MLA-3 turn network. Figure 16 shows one embodiment of a routing network for the MLA-4 layer and the mechanism whereby the MLA-4 lines are accessed. Figure 17 shows three different switch embodiments. Figure 18 shows one embodiment of a routing network for the MLA-5 layer and the mechanism whereby MLA-5 lines are accessed. DETAILED DESCRIPTION An architecture and interconnect scheme for programmable logic circuits is described. In the following description, for purposes of explanation, numerous specific details are set forth, such as combinational logic, cell configuration, numbers of cells, etc., in order to provide a thorough understanding of the present invention. It will be obvious, however, to one skilled in the art that the present invention may be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form in order to avoid unnecessarily obscuring the present invention. It should also be noted that the present invention pertains to a variety of processes including but not limited to static random access memory (SRAM), dynamic random access memory (DRAM), fuse, anti-fuse, erasable programmable read only memory (EPROM), electrically erasable programmable read only memory (EEPROM), FLASH, and ferroelectric processes. Referring to Figure 1, a block diagram of a field programmable gate array logic upon which the present invention may be practiced is shown as 100. The I/O logical blocks 102, 103, 111 and 112 provide an interface between external package pins of the FPGA and the internal user logic either directly or through the I/O to Core interface 104, 105, 113, and 114. Four interface blocks 104, 105, 113, and 114 provide decoupling between core 106 and the I/O logic 102, 103, 111, and 112. Core 106 is comprised of a number of clusters 107 which are intraconnected by I-Matrix 101 and interconnected by MLA routing network 108. Control/programming logic 109 is used to control all of the bits for programming the bit and word lines. For anti-fuse or fuse technology, high voltage/current is applied to either zap or connect a fuse. For EEPROM, Flash, or ferroelectric technology, there is an erase cycle followed by a programming cycle for programming the logic states of the memory bits. In order to minimize skewing, a separate clock/reset logic 110 is used to provide clock and reset lines on a group basis. In the currently preferred embodiment, each of the clusters 107 is comprised of a 2x2 hierarchy of four cells, called a logical cluster. Figures 2A and 2B show examples of individual cells 200 and 250. Cell 200 performs multiple logic functions on two input signals (A and B) and provides an output signal X. In the currently preferred embodiment, cell 200 is comprised of an XOR gate 201, a two-input NAND gate 202, and a two-input NOR gate 203. It should be noted, however, that in other embodiments, cell 200 can include various other types and/or combinations of gates. Cell 250 is comprised of cell 200 coupled with a D flip flop cell 260. The output X of cell 200 can be programmed to connect directly to the data input D of the D flip flop gate 204 by activating switch 218. The data input D can be accessed as a third input of the combined cell 250. Each of the two input signals A and B and the D input of D flip-flop can be inverted or non-inverted, depending on the states of switches 206-211. Activating switches 206, 208 and 210 causes signals A, B and D to be driven by drivers 212-214 to gates 201-204 in a non-inverted fashion. Activating switches 207, 209, and 211 causes the input signals A, B and D to be inverted by inverters 215-217 before being passed to gates 201-204. The six switches 212-217 can individually be turned on and off as programmed by the user. Note that the XOR gate 201, NAND gate 202, and NOR gate 203 can also be used to perform XNOR. AND and OR by propagating the output signal to the next stage, whereby the signal can be inverted as discussed above. Three switches 219-221 are respectively coupled to the outputs of the three gates 201-203. Again, these switches are programmable by the user. Thereby, the user can specify which of the outputs from the gates 201-203 is to be sent to driver 224 as the output X from cell 200. The aforementioned switches 206-211, 218-221 are comprised of bi-directional, program-controlled passgates. Depending on the state of the control signal, the switches are either conducting (i.e. passes a signal on the line) or non-conducting (i.e. does not pass the signal on the line). Switches mentioned in the following sections are similarly comprised of program-controlled passgates. Referring now to Figure 3A, a logical cluster 107 is shown. In the currently preferred embodiment, logical cluster 107 is comprised of four cells 301-304 and a D flip-flop 305, twenty five switches 306-330, and five intraconnection lines 331-335. The Intraconnection lines 331-335 and switches 306-330 form the I-Matrix. I-Matrix provide connectability of the output, X, of each of the four cells 301-304, and the output X of the D flip-flop 305 to at least one input of each of the other three cells and the D flip-flop. For example, the output X of cell 301 can be connected to input A of cell 302 by enabling switches 306 and 307. Likewise, the output X of cell 301 can be connected to input B of cell 303 by enabling switches 306 and 310. Output X of cell 301 can be connected to input A of cell 304 by enabling switches 306 and 308. Output X of cell 301 can be connected to input D of the D flip-flop cell 305 by enabling switches 306 and 309. Similarly, the output X from cell 302 can be connected to input A of cell 301 by enabling switches 311 and 312. The output X from cell 302 can be connected to input A of cell 303 by enabling switches 311 and 315. The output X from cell 302 can be connected to input B of cell 304 by enabling switches 311 and 313. Output X of cell 302 can be connected to input D of the D flip-flop cell 305 by enabling switches 311 and 314. Similarly, the output X from cell 303 can be connected to input B of cell 301 by enabling switches 326 and 327. The output X from cell 303 can be connected to input A of cell 302 by enabling switches 326 and 328. The output X from cell 303 can be connected to input B of cell 304 by enabling switches 326 and 329. Output X of cell 303 can be connected to input D of the D flip-flop cell 305 by enabling switches 326 and 330. For cell 304, the output X from cell 304 can be connected to input B of cell 301 by enabling switches 316 and 317. The output X from cell 304 can be connected to input B of cell 302 by enabling switches 316 and 318. The output X from cell 304 can be connected to input A of cell 303 by enabling switches 316 and 319. Output X of cell 304 can be programmably connected to input D of the D flip-flop cell 305 by enabling switch 218 in Figure 2A. With respect to cell 305, its output is connectable to the A input of cell 301 by enabling switches 320 and 321; the B input of cell 302 by enabling switches 320 and 322; the B input of cell 303 by enabling switches 320 and 325; the A input of cell 304 by enabling switches 320 and 323; and the D input of cell 305 itself by enabling switches 320 and 324. It can be seen that each output of the cells 301-304 and of the D flip-flop 305 is connectable to the input of each of its neighboring cells and/or flip-flop inside the cluster. In the currently preferred embodiment of the present invention, each logical cluster is connectable to all the other logical clusters inside each logical block through passgate switches extending the I-Matrix from neighboring clusters inside each logical block. Figure 3B illustrates the extension of I-Matrix intraconnection lines 331-335 of the cells 301-304 and the D flip-flop 305 of a logical cluster 107 to a neighboring logical cluster 107 through the passgate switches 336-355 within the same logical block. In the currently preferred embodiment of the present invention, each logical block is connectable to all the other logical blocks of the FPGA. This is accomplished by implementing an architecture with multiple layers of interconnections. It is important to note that this multiple layers routing architecture is a conceptual hierarchy, not a process or technology hierarchy and is hence readily implementable with today's silicon process technology. The bottom most layer of interconnections is referred to as the "block connectors". A set of block connectors provides the access and interconnections of signals within an associated logical block (which is consisted of four logical clusters or 16 cells). Thereby, different sets of logical clusters within the same logical block are connectable to any of the other logical clusters within that group through the use of extended I-Matrix and/or block connectors. Again, programmable bi-directional passgates are used as switches to provide routing flexibility to the user: The next level of connections is referred to as the "level 1 Multiple Level Architecture (MLA)" routing network. The level 1 MLA routing network provides the interconnections between several sets of block connectors. Programmable passgates switches are used to provide users with the capability of selecting which of the block connectors are to be connected. Consequently, a first logical block from one set of logical block groups is connectable to a second logical block belonging to the same group. The appropriate switches are enabled to connect the block connectors of the first logical block to the routing lines of the level 1 MLA routing network. The appropriate switches of the level 1 MLA routing network are enabled to provide the connections to the block connectors of the second logical block to the routing lines of the level 1 MLA routing network. The appropriate switches are enabled to connect the routing lines of the level 1 MLA routing network that connected to the block connectors of the first and the second logical blocks. Furthermore, the user has the additional flexibility of programming the various switches within any given logical block to effect the desired intraconnections between each of the cells of any logical block. The next level of connections is referred to as the "level 2 Multiple Level Architecture (MLA)" routing network. The level 2 MLA provides the interconnections to the various level 1 MLA to effect access and connections of a block cluster. Again, bi-directional passgate switches are programmed by the user to effect the desired connections. By implementing level 2 MLA routing network, programmable interconnections between even larger numbers of logical blocks is achieved. Additional levels of MLA routing networks can be implemented to provide programmable interconnections for ever increasing numbers and groups of logical blocks, block clusters, block sectors, etc. Basically, the present invention takes a three dimensional approach for implementing routing. Signals are routed amongst the intraconnections of a logical block. These signals can then be accessed through block connectors and routed according to the programmed connections of the block connectors. If needed, signals are "elevated" to the level 1 MLA, routed through the level 1 MLA routing network, "de-elevated" to the appropriate block connectors, and then passed to the destination logical block. If level 2 MLA routing network is required, some of the signals are elevated a second time from a level 1 MLA routing network line or directly to the level 2 MLA routing network, routed to a different set of level 2 MLA routing network line, and "de-elevated" from the level 2 MLA routing network line to a Level 1 MLA routing network line. Thereupon, the signals are "de-elevated" a second time to pass the signal from the level 1 MLA to the appropriate block connectors of the destination logical block. Alternatively, the "elevation" can be achieved directly without passing through the level 1 MLA routing network. This same approach is performed for level 3, 4, 5, etc. MLAs on an as needed basis, depending on the size and density of the FPGA. Partial level n MLA can be implemented using the above discussed method to implement a FPGA with a given cell array count. Figure 4A shows an example of a logical cluster and the associated vertical block connectors within the logical block. In the currently preferred embodiment, each cell in a logical cluster is accessible from the input by two vertical block connectors and each output of the cell in a logical cluster is accessible to two of the vertical block connectors. For example, input A of cell 301 is accessible to the vertical block connectors 451 (BC-V 11) and 453 (BC-V21) through switches 467, 462 respectively, input B of cell 301 is accessible to the vertical block connectors 452 (BC-V12) and 454 (BC-V22) through switches 466, 468 respectively, output X of cell 301 is accessible to the vertical block connectors 455 (BC-V31) and 458 (BC-V42) through switches 460, 459 respectively. Input A of cell 302 is accessible to the vertical block connectors 453 (BC-V21) and 455 (BC-V31) through switches 463, 464 respectively, input B of cell 302 is accessible to the vertical block connectors 454 (BC-V22) and 456 (BC-V32) through switches 469, 470 respectively, output X of cell 302 is accessible to the vertical block connectors 452 (BC-V12) and 457 (BC-V41) through switches 461, 465 respectively. Input A of cell 303 is accessible to the vertical block connectors 451 (BC-V11) and 453 (BC-V21) through switches 485, 476 respectively, input B of cell 303 is accessible to the vertical block connectors 452 (BC-V12) and 454 (BC-V22) through switches 480, 476 respectively, output X of cell 303 is accessible to the vertical block connectors 455 (BC-V31) and 458 (BC-V42) through switches 472, 471 respectively. The input A of cell 304 is accessible to the vertical block connectors 453 (BC-V21) and 455 (BC-V31) through switches 477, 478 respectively, input B of cell 304 is accessible to the vertical block connectors 454 (BC-V22) and 456 (BC-V32) through switches 482, 484 respectively, output X of cell 304 is accessible to the vertical block connectors 452 (BC-V12) and 457 (BC-V41) through switches 475, 474 respectively. D flip-flop cell 305 input is accessible to the vertical block connectors 454 (BC-V22) and 455 (BC-V31) through switches 473, 479 respectively, output X of cell 305 is accessible to the vertical block connectors 452 (BC-V12) and 457 (BC-V41) through switches 483, 486 respectively. In similar fashion. Figure 4B shows the possible connections corresponding to horizontal block connectors and the logical cluster shown in Figure 4A. Input A of cell 301 is accessible to the horizontal block connectors 402 (BC-H12) and 404 (BC-H22) through switches 409, 413 respectively, input B of cell 301 is accessible to the horizontal block connectors 401 (BC-H11) and 403 (BC-H21) through switches 415, 416 respectively, output X of cell 301 is accessible to the horizontal block connectors 405 (BC-H31) and 408 (BC-H42) through switches 421, 428 respectively. Input A of cell 302 is accessible to the horizontal block connectors 402 (BC-H12) and 404 (BC-H22) through switches 411, 414 respectively, input B of cell 302 is accessible to the horizontal block connectors 401 (BC-H11) and 403 (BC-H21) through switches 433, 417 respectively, output X of cell 302 is accessible to the horizontal block connectors 405 (BC-H31) and 408 (BC-H42) through switches 418, 424 respectively. Input A of cell 303 is accessible to the horizontal block connectors 404 (BC-H22) and 406 (BC-H32) through switches 419, 426 respectively, input B of cell 303 is accessible to the horizontal block connectors 403 (BC-H21) and 405 (BC-H31) through switches 420, 425 respectively, output X of cell 303 is accessible to the horizontal block connectors 402 (BC-H12) and 407 (BC-H41) through switches 410 427 respectively. The input A of cell 304 is accessible to the horizontal block connectors 404 (BC-H22) and 406 (BC-H32) through switches 422,430 respectively, input B of cell 304 is accessible to the horizontal block connectors 403 (BC-H21) and 405 (BC-H31) through switches 423, 429 respectively, output X of cell 304 is accessible to the horizontal block connectors 402 (BC-H12) and 407 (BC-H41) through switches 412, 434 respectively. D flip-flop cell 305 input is accessible to the horizontal block connectors 403 (BC-H21) and 406 (BC-H32) through switches 436, 431 respectively, output X of cell 305 is accessible to the horizontal block connectors 401 (BC-H11) and 408 (BC-H42) through switches 432, 435 respectively. Figures 4A and 4B illustrate the vertical and horizontal block connectors accessing method to the upper left (NW) logical cluster inside a logical block in the currently preferred embodiment. The lower left (SW) cluster has the identical accessing method to the vertical block connectors as those of the NW cluster. The upper right (NE) cluster has similar accessing method to those of the NW cluster with respect to the vertical block connectors except the sequence of vertical block connector access is shifted. The vertical block connectors 451-458 can be viewed as chained together as a cylinder (451, 452, ..., 458). Any shift, say by 4, forms a new sequence: (455, 456, 457, 458, 451, 452, 453, 454). Instead of starting with vertical block connectors 451 and 453 accessing by cell 301 in the NW cluster as illustrated in Figures 4A, the cell 301 in the NE cluster is accessible to VBCs 455 and 457. The numbering is "shifted" by four. The access labeling of the lower right (SE) cluster to the VBCs is identical to those of NE cluster. Similarly, the horizontal block connectors access to the NW cluster is identical to those of the NE cluster and the SW cluster is identical to the SE cluster while the horizontal block connectors access to the SW cluster is shifted by four compared with those of NW cluster. In the currently preferred embodiment, sixteen block connectors are used per logical block (i.e. four clusters, or a 4x4 cell array). Adding a level 1 MLA routing network allows for the connectability for a block cluster (an 8x8 cell array). Adding level 2 MLA routing network increases the connectability to a block sector (16x16 cell array). Additional levels of MLA routing network increases the number of block sectors by factors of four while the length (or reach) of each line in the MLA routing network increases by factors of two. The number of routing lines in the level 2 MLA is increased by a factor of two; since the number of block sectors increased by a factor of four, on a per unit area basis, the number of routing lines in the next level of hierarchy actually decreases by a factor of two. Figure 5A shows a logical block with associated sixteen block connectors and level 1 MLA routing lines associated with the logical block. The sixteen block connectors 501-516 are depicted by heavy lines whereas the sixteen level 1 MLA routing network lines 517-532 are depicted by lighter lines. Note that the length or span of the block connectors terminates within the logical block while the length of the level 1 MLA routing network lines extends to neighboring logical blocks (twice the length of the block connectors). Both block connectors and level 1 MLA routing network lines are subdivided into horizontal and vertical groups: vertical block connectors 501-508, horizontal block connectors 509-516, vertical level 1 MLA routing network lines 517-524, and horizontal level 1 MLA routing network lines 525-532. In the currently preferred embodiment, there are twenty four level 1 MLA turn points for the sixteen level 1 MLA routing network lines within the logical block. In Figure 5A, the twenty four turn points are depicted as clear dots 541-564. A MLA turn point is a programmable bi-directional passgate for providing connectability between a horizontal MLA routing network line and a vertical MLA routing network line. For example, enabling level 1 MLA turn point 541 causes the horizontal level 1 MLA routing network line 526 and vertical level 1 MLA routing network line 520 to become connected together. Figure 5B shows level 1 MLA turn point 541. Switch 583 controls whether level 1 MLA routing network line 526 is to be connected to level 1 MLA routing network line 520. If switch is enabled, then level 1 MLA routing network line 526 is connected to level 1 MLA routing network line 520. Otherwise, line 526 is not connected to line 520. Switch 583 is programmable by the user. The turn points are placed as pair-wise groups with the objective of providing switching access connecting two or more block connectors first through the block connector to level 1 MLA exchange networks and then connecting selected level 1 MLA routing lines by enabling the switches. The level 1 MLA lines are used to connect those block connectors that reside in separate logical blocks within the same block cluster. Referring back to Figure 5A, there are eight block connector to level 1 MLA exchange networks 533-540 for each logical block. These exchange networks operate to connect certain block connectors to level 1 MLA lines as programmed by the user. Figure 5C shows the exchange network 537 in greater detail. The block connector to level 1 MLA routing exchange network has eight drivers 575-582. These eight drivers 575-582 are used to provide bi-directional drive for the block connectors 501, 502 and level 1 MLA lines 517, 518. For example, enabling switch 565 causes the signal on block connector 501 to be driven by driver 575 from the level 1 MLA line 517. Enabling switch 566 causes the signal on level 1 MLA line 517 to be driven by driver 576 from the block connector 501. Enabling switch 567 causes the signal on block connector 501 to be driven by driver 577 from the level 1 MLA line 518. Enabling switch 568 causes the signal on level 1 MLA line 518 to be driven by driver 578 from the block connector 501. Similarly, enabling switch 569 causes the signal on block connector 502 to be driven by driver 579 from the level 1 MLA line 517. Enabling switch 570 causes the signal on level 1 MLA line 517 to be driven by driver 580 from the block connector 502. Enabling switch 571 causes the signal on block connector 502 to be driven by driver 581 from the level 1 MLA line 518. Enabling switch 572 causes the signal on level 1 MLA line 518 to be driven by driver 582 from the block connector 502. Switch 573 is used to control whether a signal should pass form one block connector 501 to the adjacent block connector 584 belonging to the adjacent logical block. Likewise, switch 574 is used to control whether a signal should pass form one block connector 502 to the adjacent block connector 585 belonging to the adjacent logical block. Figure 6 shows the routing network for a block cluster. The block cluster is basically comprised of four logical blocks which can be interconnected by the level 1 MLA exchange networks 533-540. It can be seen that there are thirty-two level 1 MLA routing network lines. Figure 7A shows the block diagram for a block sector. The block sector is comprised of four block clusters 701-704. As discussed above, the block clusters are interconnected by block connectors and level 1 MLA routing network lines. In addition, the block sector is also comprised of sixty-four level 2 MLA routing network lines and sixty-four level 2 to level 1 exchange networks to provide connectability between level 1 MLA routing network and level 2 MLA routing network. The level 1 to level 2 MLA routing exchange networks are depicted by rectangles in Figure 7A. Furthermore, there are forty-eight level 2 MLA turn points associated with each of the four logical blocks within the block sector. Consequently, there are one hundred and ninety-two level 2 MLA turn points for the block sector. Figure 7B shows a sample level 1 to level 2 MLA routing exchange network 705. It can be seen that switch 710 is used to control whether a signal should pass between level 1 MLA line 709 and level 2 MLA line 708. Switch 711 is used to control whether a signal should pass between level 1 MLA line 709 and level 2 MLA line 707. Switch 712 is used to control whether a signal should pass between level 1 MLA line 706 and level 2 MLA line 708. Switch 713 is used to control whether a signal should pass between level 1 MLA line 706 and level 2 MLA line 707. Switch 714 is used to control whether a signal should pass form one level 1 MLA line 709 to the adjacent level 1 MLA line 716 belonging to the adjacent block cluster. Likewise, switch 715 is used to control whether a signal should pass form one level 1 MLA line 706 to the adjacent level 1 MLA line 715 belonging to the adjacent block cluster. Figure 8A shows a sector cluster. The sector cluster is comprised of four block sectors 801-804 with their associated block connectors, level 1, and level 2 MLA routing network lines and exchange networks. In addition, there are one hundred and twenty-eight level 3 MLA routing network lines, providing connectability between the level 2 MLA lines that belong to different block sectors 801-804 within the same sector cluster 800. There are ninety-six level 3 MLA turn points associated with the level 3 MLA lines for each of the block sector 801-804 (i.e. three hundred and eighty-four total level 3 MLA turn points for the sector cluster). Furthermore, there are thirty-two level 2 to level 3 MLA routing exchange networks associated with each of the four block sector 801-804. Hence, there are total of one hundred and twenty-eight level 3 MLA routing exchange network for providing programmable connectability between the various level 2 and level 3 MLA lines. Figure 8B shows an example of a level 2 to level 3 MLA routing exchange network 805. It can be seen that enabling switch 810 causes a signal on the level 2 MLA line 808 to be connected to the level 3 MLA line 806. Disabling switch 810 disconnects the level 2 MLA line 808 from the level 3 MLA line 806. Enabling switch 811 causes a signal on the level 2 MLA line 808 to be connected to the level 3 MLA line 807. Disabling switch 811 disconnects the level 2 MLA line 808 from the level 3 MLA line 807. Likewise, enabling switch 812 causes a signal on the level 2 MLA line 809 to be connected to the level 3 MLA line 806. Disabling switch 812 disconnects the level 2 MLA line 809 from the level 3 MLA line 806. Enabling switch 813 causes a signal on the level 2 MLA line 809 to be connected to the level 3 MLA line 807. Disabling switch 813 disconnects the level 2 MLA line 809 from the level 3 MLA line 807. In the present invention, larger and more powerful FPGAs can be achieved by adding additional logic sector clusters which are connected by additional levels of MLA routing networks with the corresponding MLA turn points and exchange networks. In one embodiment of the present invention, each of the five I-Matrix lines (331-335, Figure 3A) can be extended to provide connectability between two adjacent I-Matrix lines belonging to two different clusters. The passgate switches 336-340, 341-345, 346-350, and 351-355 in Figure 3B are examples of four different sets of I-Matrix line extension switches. This provides further flexibility by providing the capability of routing a signal between two adjacent clusters without having to be routed through the use of block connectors. Similarly, block connectors can be extended to provide connectability between two adjacent block connectors belonging to two different logical blocks. Switch 573 of Figure 5C illustrates such block connector extension connecting block connector 501 to block connector 584 through switch 573. This provides further flexibility by providing the capability of routing a signal between two adjacent logical blocks without having to be routed through the level 1 MLA lines and associated MLA exchange networks. This concept can be similarly applied to the level 1 MLA lines as well. Switch 714 of Figure 7B shows an example where level 1 MLA line 709 is extended to connect to level 1 MLA line 716 by enabling switch 714. This provides further flexibility by providing the capability of routing a signal between two adjacent block clusters without having to be routed through the level 2 MLA lines and associated MLA exchange networks. Figure 9 shows one embodiment of a hierarchical multiple level routing network for providing routability between the logical blocks and the MLA levels. Eight logical blocks 901-908 are shown. Associated with each of the logical blocks 901-908 are a plurality of block connectors. In the currently preferred embodiment, there are eight horizontal and eight vertical block connectors associated with each of the logical blocks 901-908. For clarity and ease of comprehension, the block connectors corresponding to an individual logical block is represented by a single line (e.g., block connectors 909-916 respectively correspond to logical blocks 901-908) and only the horizontal block connectors are shown. In turn, each of the block connectors 909-916 are respectively coupled to programmable bi-directional drivers 917-924. Consequently, block connectors 909-916 can be programmed to be coupled bi-directionally to the MLA-1 lines 925-928. For example, exchange network 917 can be programmed to couple one of the block connectors 909 of logical block 901 to the MLA-1 line 925. Additional programmable bi-directional drivers 929-932 are used to provide interconnections between the MLA-1 lines 925-928 and the next MLA level, MLA-2 lines 933-934. Programmable bi-directional drivers 935-936 selectively provide interconnections between the MLA-2 lines 933-934 and the MLA-3 line 937. This hierarchical interconnection scheme can be repeated for additional multiple MLA levels. Figure 10 shows another embodiment of a hierarchical multiple level routing network for providing routability between the logical blocks and the MLA levels. This embodiment is similar to the routing network shown in Figure 9, except that the block connectors can be directly connected to any of the MLA levels and bypassing any intervening MLA level. Eight logical blocks 1001-1008 are shown. Associated with each logical block are a plurality of block connectors 1009-1016. Programmable bi-directional drivers 1017-1024 are used to selectively couple the block connectors 1009-1016 to the block connector tabs 1025-1032. The block connector tabs 1025-1032 are used as junction points from which connections can be made to multiple MLA layers. Programmable bi-directional driver sets (1033-1035), (1036-1038), (1039-1041), (1042-1044), (1045-1047), (1048-1050), (1051-1053), (1054-1056), correspond to block connector tabs 1025-1032, respectively. Each of these driver sets enables their respective logical block to be connected to either the MLA-1 line 1061, MLA-2 line 1062, or MLA-3 line 1063 without requiring it to pass through any intervening MLA lines. For example, logical block 1001 can be connected to the MLA-1 line 1061 by selectively activating drivers 1017 and 1033. Logical block 1001 can also be connected to the MLA-2 line 1062 by selectively activating drivers 1017 and 1034. Note that in this embodiment, logical block 1001 can be connected to the MLA-2 line 1062 without having to first be connected to the MLA-1 line 1061. Furthermore, logical block 1001 can be connected to the MLA-3 line 1063 by selectively activating drivers 1017 and 1035. Note that in this embodiment, logical block 1001 need not be connected to either the MLA-1 nor the MLA-2 layers in order for it to be connected to the MLA-3 layer. By directly connecting the logical block to the desired MLA layer, the speed of the overall routing network is improved. Furthermore, speed and routing flexibility can be enhanced by directly connecting two or more adjacent logical blocks. Thereby, adjacent logical blocks can communicate without having to be routed over any of the MLA layers. For example, logical blocks 1001 and 1002 can be connected together via the programmable bi-directional driver 1057; logical blocks 1003 and 1004 can be connected via driver 1058; and logical blocks 1005-1007 can be connected via drivers 1059-1060. This hierarchical routing scheme can readily be any number of logical blocks and MLA layers. In addition, a passgate 1064 can be included to couple block connector 1010 corresponding to logic block 1002 to block connector 1011 corresponding to logic block 1003. Figure 11 shows a block diagram of one embodiment of the hierarchical routing network wherein two groups of block connectors access the same MLA lines. A first group of logical blocks 1101-1104 and a second group of logical blocks 1105-1108 are shown. The first group of logical blocks 1101-1104 can be selectively connected to the MLA-1 layer 1109 and 1121, MLA-2 layer 1110, MLA-3 layer 1111, and MLA Tab 1112 via block connector tabs 1113-1116. Similarly, the second group of logical blocks 1105-1108 can be selectively connected to the MLA-1 layer 1109 and 1121, MLA-2 layer 1110, MLA-3 layer 1111, and MLA Tab 1112 via their respective block connector tabs 1117-1120. Figure 12 shows a block diagram of part of the multiple level routing network which encompasses Block Connectors to the MLA-3 Level with MLA Tabs for higher levels of routing network (the I-Matrix is not shown). Figure 12 shows the interconnections of one set of Block Connectors and its corresponding higher levels of MLAs in the horizontal direction. There is also a corresponding perpendicular (e.g., vertical) group of routing network interconnecting the Block Connectors and the associated MLAs. This perpendicular group is not shown in Figure 12 in order to avoid obscuring the present invention. Note that there is a corresponding copy of the routing network for each and every Block Connector and associated MLAs of the FPGA. Shown in Figure 12 are thirty-two blocks 1201-1232. Each block is associated with a distinct and adjacent block along with two BC tabs (e.g., one horizontal and one vertical). Each of the Block Connectors 1201-1232 are coupled to two selectable BC Tabs via a programmable switch. For example, block connector 1201 is coupled to selectable BC Tab 1233 through programmable switch 1234. The second group of BC Tabs, which is perpendicular (e.g., vertical) to the first BC Tab group is not shown. A similar BC Tab interconnection scheme exists for block connectors 1217-1232 (both horizontally and vertically). For each BC Tab, there are bi-directional programmable drivers connectable to the MLA-1 routing lines. For example, BC Tab 1233 is selectively connectable to the MLA-1 routing line 1235 via drivers 1236. These drivers can either be parallel to or perpendicular to the corresponding BC Tabs. In the currently preferred embodiment, the number of MLA-1 lines is half the number of Block Connectors, since for each Block Connector, there is a corresponding MLA-1 line plus another MLA-1 line which is perpendicular to the first MLA-1 line. Each MLA-1 line is connectable through programmable means to the corresponding Block Connector, MLA-2, and MLA-3 lines through their corresponding BC Tab. Note that the MLA-1 routing network together with I-Matrix lines and Block Connectors form the routing resources in a 2 x 2 Block area. This format enhances more complex logic function formation accessing and interconnecting the cells. Furthermore, the MLA-1 routing network, in addition to both I-Matrix lines and Block Connectors, become additional bi-directionally programmable access lines that can serve as access ports for the implementation of even more complex logic functions through connections by other MLA lines or Block Connectors from outside of the 2 x 2 Block area. By using programmable switches, the I-Matrix lines and block connectors can be selectively accessed which are not necessarily adjacent or congruent to the 2 x 2 Block areas. Hence, the total number of routing segments including I-Matrix lines, Block connectors, and MLA-1 lines grow geometrically when the growth is from a Block to 2 x 2 Blocks. For each BC Tab, there is bi-directionally programmable drivers connectable to the MLA-2 routing lines. For example, block connector tab 1233 is connectable to the MLA-2 line 1237 via drivers 1238. The MLA-2 can either be parallel to or perpendicular to the corresponding BC Tabs. In the currently preferred embodiment, the number of MLA-2 lines is half the number of MLA-1 lines. Each MLA-2 line is connectable through programmable means to the corresponding Block Connector, MLA-1, and MLA-3 lines through the corresponding BC Tab. The MLA-2 routing network together with I-Matrix lines, Block Connectors and MLA-1 routing network form the routing resources in a 4 x 4 Block area for more complex logic function formation accessing and for interconnecting the cells. In this case, the MLA-2 routing network, in conjunction with the I-Matrix lines, Block Connectors and MLA-1 lines, become additional bi-directionally programmable access lines that can serve as access ports for the implementation of even more complex logic functions through connections with other MLA lines or Block connectors from outside of the 4 x 4 Block area. By means of programmable switches, the access need not necessarily be adjacent or congruent to the 4 x 4 Block area. The total number of routing segments including I-Matrix lines, Block Connectors, MLA-1 lines, and MLA-2 lines in a 4 x 4 Block unit grows proportional to the increase in logic cells. The increase in the total number is geometrical when the growth is from a Block to 4 x 4 Blocks. Similarly, for each BC Tab, there is bi-directionally programmable drivers connectable to MLA-3 routing lines. For example, BC Tab 1233 is connectable to the MLA-3 line 1239 via drivers 1240. The MLA-3 routing line can either be parallel to or perpendicular (e.g., horizontal or vertical) to the corresponding BC Tabs. In the currently preferred embodiment, the number of MLA-3 lines is half the number of MLA-2 lines. Each MLA-3 line is connectable through programmable means to the corresponding Block Connector, MLA-1, and MLA-2 lines through the corresponding BC Tab. The MLA-3 routing network together with I-Matrix lines, Block Connectors, MLA-1 routing network and MLA-2 routing network form the routing resources in a 8 x 8 Block area for more complex logic function formation accessing and interconnecting the cells. The MLA-3 routing network, in addition to both I-Matrix lines, Block Connectors, MLA-1 lines and MLA-2 lines, become additional bi-directionally programmable access lines that can serve as access ports for the implementation of even more complex logic functions through connections by other MLA lines or Block Connectors that are outside of the 8 x 8 Block area and are not necessarily adjacent or congruent to the 8 x 8 Block area through programmable means. Hence, the total number of routing segment including I-Matrix lines, Block Connectors, MLA-1 lines, MLA-2 lines and MLA-3 lines in an 8 x 8 Block unit grows proportional to the increase in logic cells. This increase is geometrical when the growth is from a Block to 8 x 8 Blocks. In addition, for each BC Tab, there is bi-directionally programmable drivers connectable to MLA Tabs. For example, BC Tab 1233 is connectable to the MLA Tab 1241 via drivers 1242. The MLA Tabs can either be parallel to or perpendicular to the corresponding BC Tabs. Each bi-directionally programmable driver (e.g., driver's 1236, 1238, 1240, 1242, etc.) can be either passgate controlled through programmable means; bi-directional drivers with passgates controlled through programmable means; a tri-state controlled through programmable means in one direction and passgate or driver with a passgate controlled through programmable means; or two tri-states in opposite directions controlled through programmable means. The choice is a function of speed and density requirements. In one embodiment, each Block Connector and BC Tab have extensions to the adjacent Blocks. For example, block 1201 is connectable to block 1202 via programmable switch 1243. BC Tab 1244 is connectable to BC Tab 1245 via programmable switch 1246. It should be noted that additional extensions for MLA lines can be implemented in order to extend the routing range without having to use higher level MLA lines. Multiple variations to the routing network shown in Figure 12 are possible. For example, to increase routing resources and hence routability, the MLA-1 routing network can be replaced by making two copies of the MLA-2 routing network. On the other hand, if the objective is to minimize the routing area, one embodiment minimizes the amount of programming bits by replacing the MLA-1 routing network with a copy of the MLA-2 routing network. These kinds of variations can be applied to a mixture of other levels. Another embodiment is to off-set one or more of the MLA lines. For example, in Figure 12, the 1247 is accessible by BC Tabs 1245, 1248, 1249, and 1250. The MLA-1 line 1247 can be shifted by one block to become accessible by BC Tabs 1248, 1251, 1250, and 1252 instead. All other MLA-1 lines can be thusly shifted. This can also be applied to other MLA level(s). Figure 13 shows an MLA-1 turn network. Four logical blocks 1301-1304 are shown. These four logical blocks are connected to each of the MLA-1 lines of sets 1305-1308. Each of the MLA-1 lines is connectable through a programmable means (e.g., turn points 1309) to all the perpendicular MLA-1 lines, except the corresponding perpendicular MLA-1 line. For example, the horizontal MLA-1 line 1310 is connectable to the vertical MLA-1 line 1311 via turn point 1312. The purpose for the MLA-1 lines is to connect a set of Block Connectors together that is within the MLA-1 routing network range. In the case of connecting corresponding Block Connectors within a four-Blocks area, as shown in Figure 13, the connection(s) can be made through either the Block Connector extension or through a BC Tab to one of the corresponding MLA-1 line, without having to resort to using two perpendicular MLA-2 lines through turn points. In one embodiment, the number of turn points is reduced. This restricts the turn flexibility but also reduces both the loading on the MLA-1 lines and the area required to lay out the design. However, routing flexibility and routability may be affected. Figure 14 shows an MLA-2 turn network. As can be seen, each MLA-2 line is connectable through programmable means to every MLA-2 lines which are perpendicular to the MLA-2 line. For example, the vertical MLA-2 line 1401 is connectable to the horizontal MLA-2 line 1402 through turn point 1403. In other embodiments, the turn flexibility can be made more restrictive by reducing the number of turn points. This will reduce both the loading on the MLA-2 line and the area required to lay out the design. However, routing flexibility and routability may be affected. Figure 15 shows an MLA-3 turn network. Each MLA-3 line is connectable through programmable means to all the perpendicular MLA-3 lines. For example, the vertical MLA-3 line 1501 is connectable to the horizontal MLA-3 line 1502 through turn point 1503. The turn flexibility can be made more restrictive by reducing the number of turn points. This will reduce both the loading on the MLA-3 line and the area required to lay out the design. However, routing flexibility and routability may be affected. Figure 16 shows one embodiment of a routing network for the MLA-4 layer and the mechanism whereby the MLA-4 lines are accessed. Figure 16 shows four 8 x 8 Blocks 1621-1624 (for a total of 16 x 16 Blocks). Associated with the four 8 x 8 Blocks 1621-1624 are four horizontal and four vertical groups of MLA Tabs. In the currently preferred embodiment, the MLA-4 lines and MLA Tabs are 8-bits wide. Since each Block has eight corresponding Block Connectors, each MLA Tab is shown to be eight lines wide where each of the lines corresponds to one of the 8 Block Connectors as shown earlier in Figure 12. In the currently preferred embodiment, there are four vertical and four horizontal MLA-4 lines, each of which is eight lines wide. Thus, the number of MLA-4 lines is one-fourth the number of MLA-3 lines. Each MLA-4 line is connectable through programmable means to the corresponding Block Connector, MLA-1, MLA-2 and MLA-3 lines. The desired connectivity is made through the corresponding MLA Tab and the BC Tab. The MLA-4 routing network together with the I-Matrix lines, Block Connectors, MLA-1 routing network. MLA-2 routing network and MLA-3 routing network, form the routing resources in a 16 x 16 Block area for more complex logic function formation accessing and interconnecting of the cells. In one embodiment, the MLA-4 routing network, in addition to both I-Matrix lines, Block Connectors, MLA-1 lines, MLA-2 lines and MLA-3 lines become additional bi-directionally programmable access lines that can serve as access ports for the implementation of even more complex logic functions through connections by other MLA lines of Block Connectors from outside of the 16 x 16 Block area through programmable means. These other MLA lines or block connectors need not necessarily be adjacent or congruent to the 16 x 16 Block area. The total number of routing segments including I-Matrix lines, Block connectors, MLA-1 lines, MLA-2 lines, MLA-3 lines and MLA-4 lines in a 16 x 16 Block unit grows proportional to the increase in logic cells. The increase in size is geometrical when the growth is from a Block to 16 x 16 Blocks. From each MLA Tab there is a corresponding MLA-4 line connectable to the MLA Tab via a switch. For example, MLA Tab 1601 is connectable to MLA-4 line 1602 via switch 1603. Similarly, MLA Tab 1601 is connectable to MLA-4 line 1604 via switch 1605; MLA-4 line 1606 via switch 1607; and MLA-4 line 1608 via switch 1609. Likewise, MLA Tab 1610 is connectable to MLA-4 lines 1611-1614 via switches 1615-1618, respectively. Each MLA Tab in any one of the four corners is connectable through programmable means to all the corresponding MLA Tabs in all four corners through the vertical or the horizontal MLA-4 lines. Figure 17 shows three different switch embodiments 1701-1703. In general, the switch is a bi-directionally programmable driver network which can be a simple bi-directional passgate, or any of the bi-directional driver configurations 1701-1703. Figure 18 shows one embodiment of a routing network for the MLA-5 layer and the mechanism whereby MLA-5 lines are accessed. Sixteen 8 x 8 Blocks are shown. Associated with each of the 8 x 8 Blocks are four horizontal and four vertical MLA Tabs, which are the same as the MLA Tabs shown in Figure 16. When the 16 x 16 Blocks (as shown in Figure 16) are grouped as a unit, the next higher level, which consists of 32 x 32 Blocks, is formed. Associated with each of the four 16 x 16 corner units are four horizontal and four vertical MLA-5 lines, each 8-bit wide. These lines are shared by the adjacent corner units, as shown in Figure 18. Thus, the number of MLA-5 lines is half the number of MLA-4 lines. Each MLA-5 line is connectable through programmable means to the corresponding Block Connector, MLA-1, MLA-2, MLA-3 and MLA-4 lines through the corresponding MLA Tab and the BC Tab. The MLA-5 routing network together with I-Matrix lines, Block Connectors, MLA-1 routing network, MLA-2 routing network, MLA-3 routing network and MLA-4 routing network form the routing resources in a 32 x 32 Block area for more complex logic function formation accessing and interconnecting the cells. Furthermore, the MLA-5 routing network, in addition to both I-Matrix lines, Block Connectors, MLA-1 lines, MLA-2 lines, MLA-3 lines and MLA-4 lines can be used as additional bi-directionally programmable access lines that can serve as access ports for the implementation of even more complex logic functions through connections by other MLA lines or Block Connectors from outside of the 32 x 32 Block area (which need not necessarily be adjacent or congruent to the 32 x 32 Block area) through programmable means. The total number of routing segments including I-Matrix lines, Block Connectors, MLA-1 lines, MLA-2 lines, MLA-3 lines, MLA-4 lines and MLA-5 lines in a 32 x 32 Block unit grows proportional to the increase in logic cells. This increase is geometrical when the growth is from a Block to 32 x 32 Blocks. From each MLA Tab there is a corresponding MLA-5 line connectable to the MLA Tab via a switch. The switch is a bi-directionally programmable driver network which can be a simple bi-directional passgate, or any of the bi-directional driver configurations as shown in Figure 17. In addition, turn points are incorporated where the vertical MLA-5 lines intersect the horizontal MLA-5 lines through programmable means. Each MLA Tab in any one of the four corners is connectable through programmable means to all the corresponding MLA Tabs in all four corners. This is implemented by a combination of programmable connections to the vertical and the horizontal MLA-5 lines plus use of the turn points. Higher levels of MLA networks can be developed by programmable access through the MLA Tabs or by introducing another new intermediate MLA Tabs. In such instances, the number of MLA lines is a fraction of the next lower level MLAs. The total number of routing segments including I-Matrix lines, Block Connectors, MLA-1 lines, MLA-2 lines, MLA-3 lines, MLA-4 lines, MLA-5 lines and higher levels of MLA lines, and the corresponding number of n x n Block unit grows proportional to the increase in logic cells. This increase is geometrical when the growth is from a Block to the n x n Blocks. Thus, an architecture with an intraconnect and interconnect scheme for programmable logic circuits is disclosed.

Claims: A programmable logic circuit comprising: a plurality of logic blocks, each logic block comprising a plurality of configurable cells configured to perform logic functions on logic signals; a first set of routing lines selectively coupling the configurable cells of a logic block wherein said first set of routing lines is selectively coupled to the input ports and output ports of the configurable cells of said logic block through a first set of switches; a second set of routing lines, said second set of routing lines having different spans than said first set of routing lines; a first routing line and a second routing line of said second set of routing lines, offset from each other by at least one logic block, wherein said first routing line is selectively coupled to at least one routing line of a first set of routing lines of a first logic block and to at least one routing line of a first set of routing lines of a second logic block through a second set of switches, said second logic block located adjacent to said first logic block, said first routing line spanning at least the lengths of said first and said second logic blocks, and said second routing line is selectively coupled to at least one routing line of the first set of routing lines of said second logic block and to at least one routing line of the first set of routing lines of a third logic block through said second set of switches, said third logic block located adjacent to said second logic block, said second routing line spanning at least the lengths of said second and said third logic blocks. The programmable logic circuit as set forth in claim 1, wherein the first set and the second set of switches comprise components selected from the group comprising switches, programmable passgates and program controlled drivers/receivers. The programmable logic circuit as set forth in claim 1, wherein said second set of routing lines have greater spans than said first set of routing lines. The programmable logic circuit as set forth in claim 1, further comprising a third set of routing lines, having different spans than said first set of routing lines, selectively coupling said first sets of routing lines wherein a third routing line of said third set of routing lines selectively couples to at least one routing line of a first set of routing lines of said first logic block and to at least one routing line of a first set of routing lines of said second logic block through a third set of switches. The programmable logic circuit as set forth in claim 4, wherein said third set of routing lines have greater spans than said first set of routing lines. The programmable logic circuit as set forth in claim 4, wherein a fourth routing line of said third set of routing lines, offset from said third routing line by at least a logic block, selectively couples to at least one routing line of a first set of routing lines of said second logic block and to at least one routing line of a first set of routing lines of said third logic block through said third set of switches. The programmable logic circuit as set forth in claim 4, wherein said third set of routing lines have greater spans than said second set of routing lines. The programmable logic circuit as set forth in claim 1, further comprises at least one fourth set of routing lines, having different spans than said second set of routing lines, selectively coupling said second of routing lines to said at least one fourth set of routing lines through a fourth set of switches. The programmable logic circuit as set forth in claim 1, wherein the first set of routing lines is selectively coupled to at least two routing lines of said second set of routing lines through said second set of switches. The programmable logic circuit as set forth in claim 1, wherein a first portion of routing lines of said first set of routing lines is orthogonal to a second portion of routing lines of said second first set of routing lines. The programmable logic circuit as set forth in claim 1, wherein a first portion of routing lines of said second set of routing lines in a first dimension is selectively coupled to a second portion of routing lines of said second set of routing lines in a second dimension through a fifth set of switches. The programmable logic circuit as set forth in claim 4, wherein a first portion of routing lines of said third set of routing lines in a first dimension is selectively coupled to a second portion of routing lines of said third set of routing lines in a second dimension through a sixth set of switches. A method for programming a programmable logic circuit comprising: a first set of routing lines selectively coupling configurable cells of a logic block of a plurality of logic blocks wherein said first set of routing lines is selectively coupled to the input ports and output ports of the configurable cells of said logic block; a second set of routing lines, said second set of routing lines having different spans than said first set of routing lines; selectively coupling a first routing line of the second set of routing lines to at least one routing line of a first set of routing lines of a first logic block and to at least one routing line of a first set of routing lines of a second logic block, said second logic block located adjacent to said first logic block, said first routing line spanning at least the lengths of said first and said second logic blocks; and selectively coupling said second routing line to at least one routing line of the first set of routing lines of said second logic block and to at least one routing line of the first set of routing lines of a third logic block, said third logic block located adjacent to said second logic block, said second routing line spanning at least the lengths of said second and said third logic blocks. The method as set forth in claim 13, further comprising a third routing line of said third set of routing lines selectively coupling at least one routing line of a first set of routing lines of said first logic block and at least one routing line of a first set of routing lines of said second logic block. The method as set forth in claim 13, further comprising selectively coupling a fourth routing line of said third set of routing lines, offset from said third routing line by at least a logic block, to at least one routing line of a first set of routing lines of said second logic block and to at least one routing line of a first set of routing lines of said third logic block. The method as set forth in claim 13, further comprising selectively coupling said second set of routing lines to said at least one fourth set of routing lines having different spans than said second set of routing lines. The method as set forth in claim 13, further comprising selectively coupling the first set of routing lines to at least two routing lines of said second set of routing lines. The method as set forth in claim 13, further comprising selectively coupling a first portion of routing lines of said second set of routing lines in a first dimension to a second portion of routing lines of said second set of routing lines in a second dimension.

Inventors: TING BENJAMIN S, TING, BENJAMIN S.
Applicants: BTR INC, BTR, INC.
Application year: 1995
Main classification: H03K19
IPC codes: H03K19