Logic module with configurable combinational and sequential blocks

Abstract: A logic module includes a first (12) and a second (14) two-input multiplexer each having first and second data inputs. Both the first and second multiplexer (12,14) include a select input (5), both of which are connected to the output of a two-input logic gate of a first type (3,4) having first and second data inputs. The inputs to the first and second two-input multiplexers (12,14) are sourced with data signals (D00,...,D11) from a first group. One input of each of the logic gates is sourced from a data signal of a second group (A) and the other input of each of the logic gates is sourced from a data signal of a third group (B). A third two-input multiplexer (40) has its first and second data inputs (36,38) connected the outputs of the first and second multiplexers (12,14), respectively. A select input (42) of the third two-input multiplexer (40) is connected to the output of a two-input logic gate of a second type (48) having first and second data inputs. The output of the third two-input multiplexer (40) is connected to a first data input of a fourth two-input multiplexer (60) having a HOLD1 input coupled to its select input (62). Its output is and a CLEAR input are presented to an AND gate (70) whose output is connected to the second data input (74) of the fourth two-input multiplexer (60) and to the first data input (74) of a fifth two-input multiplexer (78). The select input (80) of the fifth two-input multiplexer is connected to a HOLD2 input. Its output and the CLEAR input are presented to an AND gate (88) whose output is connected to the second data input (92) of the fifth two-input multiplexer (78) and to an output node (94). The CLEAR, HOLD1 and HOLD2 inputs are defined by combinations of signals from a data signal of a third group which may contain a data signal of one of the other groups.

Description: The present invention relates to digital electronic circuits. More specifically, the present invention relates to circuits for performing logic functions in user-programmable integrated circuits, and to circuits for implementing a wide variety of user-selectable combinatorial and sequential logic functions. Programmable logic blocks which are capable of performing a selectable one of a plurality of user-selectable logic functions are known in the prior art. U.S. Patent No. 4,910,417 to El Gamal et al., assigned to the same assignee as the present invention, and U.S. Patent No. 4,453,096 to Le Can et al., disclose logic modules composed of multiplexers capable of performing a plurality of combinatorial functions. L'Onde Electrique Vol. 59, No. 11, pp 81-86 describes a universal combinatorial logic module using 3 multiplexers. While these circuits provide a degree of flexibility to the designer of user-programmable logic arrays, there is always a need for improvement of functionality of such circuits. The present invention is defined in appended claim 1. In an embodiment of the present invention, a logic module is provided having a wide variety of user-configurable combinational and sequential logic functions. In a first stage of a combinatorial section, the logic module includes a first and a second two-input multiplexer each having first and second data inputs. Both the first and second multiplexer include a select input, both of which are connected to the output of a two-input logic gate of a first type having first and second data inputs. The inputs to the first and second two-input multiplexers are sourced with data signals from a first group. One input of each of the logic gates is sourced from a data signal of a second group and the other input of each of the logic gates is sourced from a data signal of a third group. In a second stage of the combinatorial section of the logic module, a third two-input multiplexer has its first and second data inputs connected the outputs of the first and second multiplexers, respectively. A select input of the third two-input multiplexer is connected to the output of a two-input logic gate of a second type having first and second data inputs. In a first stage of a sequential section of the logic module of the present invention, the output of the third two-input multiplexer is connected to a first data input of a fourth two-input multiplexer having a HOLD1 input coupled to its select input. Its output and a low active CLEAR input are presented to an AND gate whose output is connected to the second data input of the fourth two-input multiplexer and to the first data input of a fifth two-input multiplexer in a second stage of the sequential section of the logic module of the present invention. The select input of the fifth two-input multiplexer is connected to a HOLD2 input. Its output and the CLEAR input are presented to an AND gate whose output is connected to the second data input of the fifth two-input multiplexer and to an output node. The CLEAR, HOLD1 and HOLD2 inputs are defined by combinations of signals from a data signal of a third group which may contain a data signal of one of the other groups. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of a logic module according to a presently preferred embodiment of the present invention. FIG. 2a is a diagram showing a combinatorial circuit for generating the CLEAR, HOLD1, and HOLD2 signals for the circuit of FIG. 1 from data inputs. FIG. 2b is a logic diagram in block form of a presently preferred circuit for use in performing the function of the circuit of FIG. 2a. DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT Referring first to FIG. 1, a block diagram of a presently preferred embodiment of a logic module according to the present invention, a logic module 10 is shown having configurable combinational and sequential blocks. The combinatorial portion of the logic module includes first and second sections. A first section of the logic module 10 of the present invention includes first and second two-input multiplexers 12 and 14. First two-input multiplexer includes first and second data inputs 16 and 18, select input 20 and output 22. Second two-input multiplexer has first and second data inputs 24 and 26, select input 28 and output 30. Select inputs 20 and 28 of first and second two-input multiplexers 12 and 14 are connected to the output 32 of a two-input logic gate of a first type 34 having first and second data inputs 50 and 54. Outputs 22 and 30 of first and second two-input multiplexers 12 and 14 are connected to data inputs 36 and 38 of third two-input multiplexer 40, in a second section of logic module 10. Third two-input multiplexer 40 also includes select input 42 and output 44. Select input 42 of third two-input multiplexer 40 is connected to output 46 of a two-input logic gate of a second type 48 having first and second data inputs 52 and 56. The data inputs 16, 18, 24 and 26 to the first and second two-input multiplexers are sourced with data signals from a first group of data input nodes shown in FIG. 1 as data inputs D00, D01, D10, and D11. One input of each of logic gates 34 and 48 (reference numerals 50 and 52, respectively) is sourced from a data signal of a second group shown in FIG. 1 as data input nodes A0 and A1, respectively, and the other input of each of the logic gates (reference numerals 54 and 56, respectively) is sourced from a data signal of a third group shown in FIG. 1 as data input nodes B0 and B1, respectively. The logic module 10 of the present invention offers a plurality of combinatorial functions having up to eight inputs. The function implemented by the circuit of FIG. 1 is: Z= (D00 !(A0·B0) + D01 (A0·B0)) !(A1+B1) + (D10 !(A0·B0) + D11(A0·B0)) (A1+B1) The combinatorial functions which may be implemented include AND, OR, NAND, NOR, and EX-OR. TABLE I shows the implementation of these functions using different inputs of the circuit of FIG. 1. FUNCTION A0 B0 A1 B1 D00 D01 D10 D11 C1 C2 NAND !(A·B) A B 1 X X X 1 0 1 0 A B X 1 X X 1 0 1 0 A B 0 0 1 0 X X 1 0 A B 0 0 1 0 0 0 1 0 1 A 0 B 1 1 1 0 1 0 1 A B 0 1 1 1 0 1 0 A 1 0 B 1 1 1 0 1 0 A 1 B 0 1 1 1 0 1 0 NOR !(A+B) 1 1 A B X 1 X 0 1 0 0 X A B X X 0 X 1 0 X 0 A B X X 0 X 1 0 1 A 0 B 1 0 0 0 1 0 1 A B 0 1 0 0 0 1 0 A 1 0 B 1 0 0 0 1 0 A 1 B 0 1 0 0 0 1 0 AND · (A·B) A B 0 0 0 1 X X 1 0 A B 1 X X X 0 1 1 0 A B X 1 X X 0 1 1 0 A B 0 0 0 0 1 0 1 0 1 A B 0 0 0 0 1 1 0 1 A 0 B 0 0 0 0 1 0 A 1 B 0 0 0 0 1 1 0 A 1 0 B 0 0 0 1 1 0 OR (A+B) X X A B 0 0 1 1 1 0 0 X A B 0 X 1 X 1 0 X 0 A B 0 X 1 X 1 0 1 A 0 B 0 1 1 1 1 0 1 A B 0 0 1 1 1 1 0 A 1 0 B 0 1 1 1 1 0 A 1 B 0 0 1 1 1 1 0 XOR (A· !B)+(!A· B) A 1 B 0 0 1 1 0 1 0 A 1 0 B 0 1 1 0 1 0 1 A B 0 0 1 1 0 1 0 1 A 0 B 0 1 1 0 1 0 XNOR (A·B)+(!A·B) A 1 B 0 1 0 0 1 1 0 A 1 0 B 1 0 0 1 1 0 1 A B 0 1 0 0 1 1 0 1 A 0 B 1 0 0 1 1 0 Those of ordinary skill in the art will further appreciate that different gates, such as NAND, NOR, EX-OR gates, could be used as well with slightly different results. In particular, using all like gates on the select inputs (for example, all NAND or NOR gates), increases the number of inputs on the functions (AND OR), while using a mix of gates on the select inputs (for example NAND on the first select input and NOR on the second select input as shown in FIG. 1) increases the number of functions which the module can generate. Referring again to FIG. 1, it may be seen that the sequential portion of logic module 10 also has two stages. In the first sequential stage, the output 44 of the third two-input multiplexer 40 is connected to a first data input 58 of a fourth two-input multiplexer 60 having its select input 62 driven by a HOLD1 signal from a HOLD1 control node. Its output 64 and a CLEAR signal from a CLEAR control node are presented to inputs 66 and 68 of an AND gate 70 whose output 72 is connected to the second data input 74 of the fourth two-input multiplexer and to the first data input 76 of a fifth two-input multiplexer 78, which forms the input to the second sequential stage. The select input 80 of the fifth two-input multiplexer 78 is connected to a HOLD2 signal from a HOLD2 control node. Output 82 of fifth two-input multiplexer 78 and the CLEAR signal are presented to inputs 84 and 86 of an AND gate 88 whose output 90 is connected to the second data input 92 of the fifth two-input multiplexer and to an output node 94. In a presently preferred embodiment, the CLEAR, HOLD1 and HOLD2 signals are derived by combinatorial logic from a set of data input signals. As is shown in FIG. 2a, data signals from data input nodes C1, C2 and B0 are presented to inputs 96, 98, and 100, respectively of logic combining circuit 102, which has control node outputs upon which the HOLD1, HOLD2, and CLEAR signals appear, respectively. The logic combining circuit 102 of FIG. 2a may be any logic circuit for combining the three inputs in a manner which produces outputs for the HOLD1, HOLD2, and CLEAR signals as set forth in the truth table in TABLE II. C1 C2 HOLD1 HOLD2 CLEAR 0 0 0 1 B0 0 1 1 0 B0 1 0 0 0 1 1 1 0 1 B0 FIG. 2b is a logic diagram of a presently preferred embodiment of such a circuit. Referring now to FIG. 2b, logic combining circuit 102 includes AND gate 104 with inverting input 106 and non-inverting input 108, and output 110, AND gate 112 with inverting input 114 and noninverting input 116 and output 118, EXNOR gate 120 with inputs 122 and 124 and output 126 and OR gate 128 with inputs 130 and 132 and output 134. C1 input 96 is connected to inputs 106 and 116 of AND gates 104 and 112, respectively and to input 122 of EXNOR gate 120. C2 input 98 is connected to inputs 108 and 114 of AND gates 104 and 112, respectively, and to input 124 of EXNOR gate 120. B0 input 100 is connected to input 132 of OR gate 128. The output 112 of AND gate 112 is connected to input 130 of OR gate 128. The output 110 of AND gate 104 is the HOLD1 signal, the output 126 of EXNOR gate 120 is the HOLD2 signal, and the output 134 of OR gate 128 is the clear signal. The sequential portion of the logic module of the present invention disclosed herein is configurable as a rising or falling edge flip flop with asynchronous low active clear, a transparent low or high latch with asynchronous low active clear, or as a transparent flow-through element which allows only the combinatorial section of the module to be used. All latches and flip flops are non-inverting. TABLE III illustrates the sequential functions available from the logic module of the present invention. From TABLE III, it can be seen that the sequential functions which may be performed include a negative triggered latch with low active clear, a positive triggered latch with low active clear, a negative triggered flip flop with low active clear, a positive triggered flip flop with low active clear and a flow through mode. As can be seen from FIG. 4, the states of inputs A0, D00 and D10 are restricted for positive and negative triggered latches. A0 must equal 1 and both D00 and D10 must equal 0 in order for the output to be low when the latch is in transparent mode and the clear input is active. C1 C2 FUNCTION ! CLEAR RESTRICTIONS 0 CLK Rising Edge Flip Flop B0 None CLK 1 Falling Edge Flip Flop B0 None 1 CLK High Latch with Clear B0 A0=1; D00,D10=0 CLK 0 Low Latch with Clear B0 A0=1; D00,D10=0 1 CLK High Latch -- B0=1 CLK 0 Low latch -- B0=1 1 0 Transparent -- None The two-input multiplexers and other logic components of the logic module of the present invention may be fabricated using conventional MOS and CMOS technology.

Claims: A universal logic module including: a first multiplexer (12) having a first data input (16) connected to a first data node, a second data input (18) connected to a second data node, a select input (20), and an output (22), a second multiplexer (14) having a first data input (24) connected to a third data node, a second data input (26) connected to a fourth data node, a select input (28), and an output (30), a third multiplexer (40) having a first data input (36) connected to the output (22) of said first multiplexer (12), a second data input (38) connected to the output (30) of said second multiplexer (14), a select input (42), and an output (44), a first single logic level gate (34) having a first input (50) connected to a fifth data node, a second input (54) connected to a sixth data node and an output (32) connected to the select inputs (20, 28) of said first and second multiplexers (12, 14), a second single logic level gate (48) having a first input (52) connected to a seventh data node, a second input (56) connected to an eighth data node and an output (46) connected to the select input (42) of said third multiplexer (40), a fourth multiplexer (60) having a first data input (58) connected to the output (44) of said third multiplexer (40), a second data input (74), a select input (62) connected to a first control node, and an output (64), a first AND gate (70) having a first input (68) connected to the output (64) of said fourth multiplexer (60), a second input (66) connected to a second control node, and an output (72) connected to the second data input (74) of said fourth multiplexer (60), a fifth multiplexer (78) having a first data input (76) connected to the output (72) of said first AND gate (70), a second data input (92), a select input (80) connected to a third control node, and an output (82), a second AND gate (88) having a first input (86) connected to the output (82) of said fifth multiplexer (78), a second input (84) connected to said second control node, and an output (90) connected to the second data input (92) of said fifth multiplexer (78) and to an output node (Z), means (102) for placing either a logic one or the contents of a ninth data node on said second control node in response to preselected combinations of the states of a tenth and an eleventh data node, and means (102) for placing either a logic zero or a logic one on said first control node and for placing either a logic zero or a logic one on said third control node in response to preselected combinations of the states of said tenth and eleventh data nodes. A logic module according to claim 1, wherein said first logic gate (34) is an AND gate and said second logic gate (48) is an OR gate.

Inventors: EL GAMAL ABBAS A, GALBRAITH DOUGLAS C, GREENE JONATHAN W, EL GAMAL, ABBAS A., GALBRAITH, DOUGLAS C., GREENE, JONATHAN W.
Applicants: ACTEL CORP, ACTEL CORPORATION
Application year: 1991
Main classification: H03K19
IPC codes: H03K3, G06F17, H03K19