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Question & Answer
Classification:
Date: Jan 11, 2001
Unable to control upper segments of the XSV Board bargraph LED
Q:
I recently purchased an XSV Board and I've been writing some simple VHDL code to test the various features of the board (7-segment displays, led bar graph, push buttons, etc). One of my tests was to write all 1's to the led bar graph. However, B1 is not lighting. I know that the led works because when I plug in the power supply, both B1 and B9 light up.
I've triple-checked my pin mapping and I am indeed writing a '1' to B1 (listed as pin 154 on page 28 of the XSV Board V1.0 Manual). Also, all of my dip switches are in the 'off' position.
Any suggestions on what is wrong? Is the pin number right? Could the CPLD or Flash RAM be pulling it low?
A:
The CPLD uses B0 and B1 to indicate the status on the FPGA DONE and INIT pins. You should not try to drive these segments unless you reprogram the CPLD to release them. Here is a document that describes the parallel port interface circuit programmed into the XSV Board CPLD.