detecting gnd

Jul 07, 2006 1 Replies
C

I want to make a FPGA/CPLD test board to plug into a socket to test the connectivity of the socket.



Does anyone know of a way to check that all of the gnds and powers are connected given that I want to power the test board from the socket. I need to connect an fpga pin to a GND pin (there is ten of them) so that if the connector pin is O/C it floats high but if it is connected to GND then it contributes to the GND plane and vice versa for VCC.



I don't think it can be done without several op amps and I'll have to use some power pins properly but just thought I'd ask.



Colin



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A

colin schrieb:

Sure you can do this with single PLD!

1) take a 2.5V (or 3.3V if your socket has 5V) PLD with permanent protection diodes in the chip to both GND and VCCIO - the GND diodes should present in all devices but the VCC protection diodes may only be enabled after configuration, so you may need to check datasheets or make some experiments

2) connect a bypass capacitor and parallel zener diode (2.5 or 3.3V) to the PLD GND and VCC pins

3) connect GND pins from socket to regular PLD IOs and with week pullup to VCC (if that pullup can not be enabled in the PLD)

4) connect VCC pins from socket via series resistor to PLD IO pads, add weak pulldown if not possible to enable in PLD

Thats it!

The PLD power and GND should float somewhere between the socket GND and VCC but you should be able to test all you need

if the PLD lacks the protection diodes to VCC rail you need to add those externally.

Antti

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