Abstract:
An apparatus for providing a probing interface for a circuit under test exhibits a relatively narrow profile and a vertical orientation so that it does not block access to connectors in adjacent slots. The vertical orientation is made possible by the use of a circuit material comprising alternate sections of flexible material and rigid material. Advantageously, the signal lines between the circuit card under test and its motherboard are direct and relatively short, and the probing connection points are isolated from the direct signal lines by a plurality of isolation resistors. The probing adapter includes the capability of monitoring the bus of the system under test and disassembling monitored AGP codes.

Description:
FIELD OF THE INVENTION 
     The subject invention concerns the field of expander cards in general, and specifically concerns probe adapters suitable for use with logic analyzers. 
     BACKGROUND OF THE INVENTION 
     When using many electronic test and measurement equipment products, such as, oscilloscopes, logic analyzers, communication systems protocol analyzers, spectrum analyzers, and the like, to troubleshoot a circuit under test, it is quite common to employ a circuit card extender to elevate a particular circuit card an thereby facilitate connection of test probes to the circuit under test (sometimes referred to as a System Under Test, or SUT). In the distant prior art, this feature was implemented by providing a board with a card edge connector on one end, a card edge receptacle on the other end, and a plurality of printed traces running straight across the board from the card edge to the receptacle. Probing was performed directly on the circuit board under test. 
     A probing adapter is nonintrusive hardware that allows a logic analyzer to acquire data from a bus in its own operating environment with little, if any, effect on the target system. A probing adapter comprises a circuit board and a socket for a circuit card to be tested. A probing adapter plugs into a bus receptacle on the target system and signals from the system bus flow through the probing adapter to a logic analyzer. Modern probing adapters must support logic analyzers which have the capability of monitoring a large number of channels (for example 136 channels), simultaneously. Consequently, in addition to elevating the circuit under test from its motherboard, by interposing between the circuit under test and its normal connector on the motherboard, a probing adapter also provides connection points (i.e., sockets) for high density multiconductor probes. 
     Unfortunately, prior art probing adapters suffered from several disadvantages. Among these disadvantages are: signal reflections caused by impedance mismatches due to the use of the connectors to turn the probe adapter from a vertical orientation to a horizontal orientation for use, and blocking of adjacent slots due to the horizontal orientation of the probing adapter. Moreover, prior art probing adapters do not have the capability to disassemble the AGP (Accelerated Graphics Port) code at the adapter itself. A probe adapter exhibiting these disadvantages is the FSAGP 32TE AGP Probe manufactured for Hewlett Packard Inc. by FuturePlus Systems Corporation, Colorado Springs, Colo. 
     What is needed is a probing adapter which does not block adjacent slots, which does not introduce impedance mismatches which would otherwise cause reflective events, and which has the capability to disassemble monitored AGP codes. 
     SUMMARY OF THE INVENTION 
     An apparatus for providing a probing interface for a circuit under test exhibits a relatively narrow profile and a vertical orientation so that it does not block access to connectors in adjacent slots. The vertical orientation is made possible by the use of a circuit material comprising alternate sections of flexible material and rigid material. Advantageously, the signal lines between the circuit card under test and its motherboard are direct and relatively short, and the probing connection points are isolated from the direct signal lines by a plurality of isolation resistors. The probing adapter includes the capability of monitoring the bus of the system under test and disassembling monitored AGP codes. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 shows an embodiment of a thin profile vertically oriented probing adapter according to the invention. 
     FIG. 2 shows the embodiment of FIG. 1 in use with a circuit card under test. 
     FIG. 3 shows a front view of the embodiment of FIG. 1. 
     FIG. 4 shows a simplified card representing a circuit to be tested. 
     FIG. 5 shows a rear view of the embodiment of FIG. 1. 
     FIG. 6 shows, in block diagram form, suitable circuitry for a probing adapter according to the subject invention 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIG. 1, a thin (or narrow) profile vertically oriented probing adapter 100 is shown. Adapter 100 comprises a first rigid section 105 having connector pads (not shown in FIG. 1) formed thereon for connection to a mating receptacle on a motherboard (also not shown in FIG. 1). Adapter 100 further comprises a flexible section 110 for transferring electrical signals between first rigid section 105 and a second rigid section 115, perpendicularly mounted with respect to board section 105. Adapter 100 further comprises a second flexible section 120 for coupling electrical signals between second rigid section 115 and a third rigid section 125. 
     Adapter 100 includes a mating card edge receptacle 130 mounted on second rigid section 115 for receiving a circuit card to be tested, and for supporting the circuit card to be tested in the same vertical orientation it exhibits when plugged directly into the motherboard. Adapter 100 is preferably made using a &#34;rigid-flex&#34; circuit material, which is readily available for a variety of circuit board manufacturers. 
     Many high reliability applications call for durability and high temperature which often require a rigid-flex circuit. A rigid flex is basically a flexible circuit integrated into a multilayer rigid construction. The flexible layers extend through the rigid portions allowing the holes to be plated through directly from the outside rigid layers to the internal flex layers. This is often the best solution from a packaging standpoint. The rigid sections are ideal for component and connector mounting, while protruding flexible portions allow flexing for installation and there are no connectors required at the flex-to-board interfaces. Mechanically you get the best of both worlds. The flexible portion of this material passes through the interior of the rigid sections and is superior to using connectors arranged at right angles to pass signals between perpendicularly mounted circuit boards. This is so because the impedance of the signal lines is maintained substantially constant and thus no reflective event transition is introduced. The use of rigid-flex techniques also avoids the added capacitance which would accompany the use of right angle connectors. 
     Note that the distance between the lower end of rigid section 105 and receptacle 130 is relatively short, about 1.5 inches in actual practice. This relatively short distance advantageously reduces the round trip time delay for the signals passing between the circuit under test and the motherboard. t is also important to note that there are no intervening components between the motherboard and the circuit under test. 
     Rigid section 125 may have electronic components 135 mounted thereon for specific purposes when testing specific boards. Such components are not necessary to the invention and will not be described. Rigid section 125 may also have one or more test points 140 mounted thereon for individual probing, but the main connection point for test and measurement is via one or more high density connectors 145. A probe 150, having a right angle head 155 is shown connected to high density connector 145. A bundle of test probe leads 160 connects between head 155 and probe body 150. 
     It is important to isolate the test probe from the circuit under test so as not to introduce significant loading. In this regard, each of the pins of receptacle 130 is coupled to probe head 155 via a respective series connected isolation resistor, generally designated 165. The value of each of the plurality of series connected isolation resistors 165 is preferably 180 ohms. Probing adapter 100 is held in position by mounting brackets 170 and screws or rivets 175. 
     The thin profile enables a probing adapter according to the subject invention to be used where the spacing between connectors on the motherboard is as little as 0.8 inches. This feature is extremely important because it allows testing of the circuit under test while the card in the next adjacent slot is plugged into its receptacle in the motherboard. No other probing adapter allows such operation. 
     A front view of probing adapter 100 of FIG. 1 is shown in FIG. 2 wherein elements which bare similar numbers to elements in FIG. 1 serve similar functions which will not be described again. First rigid section 205 of probing adapter 200 includes a keyway 206 for guiding insertion into a receptacle on the motherboard, and for preventing backwards insertion. Rigid section 205 has connector pads generally designated 207 plated thereon to make electrical connection to the receptacle pins when probing adapter 200 is inserted into the receptacle (not shown in this FIGURE) on the motherboard. Each of the signals on each of connector pads 207 are conveyed to the interior of rigid section 205 by way of a via (i.e., a plated through hole) generally designated 208 which makes contact with both the printed trace leading to a contact pad 207 and to the flexible circuit material occupying an interior layer of rigid section 207. 
     FIG. 3 shows a simplified representation of a circuit board to be tested. Note that it has the same keyway 306 in the same position for mating with its receptacle on the motherboard. 
     Referring to FIG. 4, a probing adapter 400 according to the invention is shown inserted into a receptacle 480 of a motherboard 490. Elements which bare similar numbers to elements in FIG. 1 serve similar functions which will not be described again. Note that a circuit board to be tested (for example, the circuit board of FIG. 3) has been inserted into test receptacle 430. Circuit board 495 is coupled to its motherboard without any intervening components over a connection run which is only about 1.5 inches in length, and should function in the same manner as if it were plugged into its motherboard receptacle directly. It is important to note from FIG. 4 that circuit boards may be plugged into adjacent motherboard receptacles 482 and 484, a valuable feature that was hereto fore unavailable to the test engineer. 
     FIG. 5 is an illustration of the rear side of probing adapter 100 of FIG. 1. Probing adapter 500 preferably includes two CPLAs (Complex Programmable Logic Arrays). The PIPE CPLA 501 keeps track of AGP bus activity when the circuit under test is operating in 1× or 2× PIPE mode. The SBA CPLA 502 tracks bus activity when the circuit under test is operating in 1× or 2× SBA mode. Jumpers 504 on probing adapter 500 allow the user to choose PIPE or SBA mode as well as 1× or 2× mode. Each of CPLA integrated circuits 501 and 502 is coupled to the system bus through the above-mentioned series coupled isolation resistor array to prevent loading of the bus. The CPLA integrated circuits monitor the bus, evaluate the state of the bits on each clock cycle and translate the bits into assembly language for display on the screen of the logic analyzer to allow the user to more easily debug the hardware or software in the system under test. 
     Referring to the block diagram of FIG. 6, AGP signals are applied at the input of the probing adapter (also referred to as the interposer connection), and are coupled to the remainder of the circuitry by isolation resistors 610 (mentioned above with respect to reference numeral 165). The isolation resistors couple the AGP signals to Data Bus Connector 650, Control Signal Latch 620, Address/Clock Bus Buffer 630, and Address Latch 640. Address Latch 640 provides address signals to SBA Mode CPLD 680. Control Signal Latch 620 provides control signals to Control Bus Connector 660 which in turn provides these signals to an externally connected logic analyzer (not shown). Control Signal Latch 620 also provides control signals to PIPE mode CPLD 670, and to SBA Mode CPLD 680. Address/Clock Bus Buffer .630 provides clock signals to Pie Mode CPLD 670 and SBA Mode CPLD 680. PIPE mode CPLD 670 provides control and queue counter signals to Control and Queue Counter connector 690 for further connection to the aforementioned logic analyzer. 
     Thus, there has been described a probing adapter device for connecting to and supporting in a vertical direction, a circuit under test. As a result of using the subject invention, one can test the circuit under operating conditions with boards inserted into adjacent receptacles on the motherboard, and one can view disassembled code on the screen of the logic analyzer. 
     While the invention has been described with respect to connection to a logic analyzer, it is herein recognized that it is also applicable to other types of test and measurement instruments, such an oscilloscope, a spectrum analyzer, or the like, and such modification is deemed to lie within the scope of the following claims.