Answers Database

PROMS: AT&T flash proms may sometimes put out incorrect data


Record #364

Product Family:  Hardware

Product Line:  1700

Problem Title:
PROMS: AT&T flash proms may sometimes put out incorrect data


Problem Description:
AT&T flash proms may sometimes put out incorrect data

AT&T PROMs are successfully read back but may output the wrong data.  As a
result, the associated fpga doesn't configure properly.


Solution 1:

CAUSE:

Power on reset is not all that consistent. The serial PROM address may not
be reset properly and the prom may begin sending data in the middle of the
stream instead of the beginning (preamble/length count).
	

SOLUTIONS:

When powering down an AT&T flash prom, VCC must go all the way to zero,
otherwise this problem may occur when power is turned back on. Try removing
the chip completely from the system and reinserting it.  If this causes the prom

to work properly again, the problem may be with VCC not turning off completely.

One solution would be to replace the AT&Tprom with a Xilinx prom.

Another possible solution is to connect the INIT pin on the FPGA to the active l
ow reset
of the serial PROM and see if that clears it.  INIT stays low while the FPGA
configuration is being cleared, then goes high when the FPGA is ready to receive
 data.
A high level on INIT would subsequently release the reset on the serial PROM.
Doing
this would allow the prom's data counter to be reset properly.






End of Record #364