Write-enable jumper instead of write-protect jumper

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Write-enable jumper instead of write-protect jumper

Postby freekheite » Fri May 05, 2006 4:09 pm

Hello CFFA fans,

On the current CFFA card V2.0, the onboard EEPROM is write-protected by having installed a jumper, called JP2.
This might be a potential risk. If the jumper ever falls off, or if its contact pins get corroded over time, the EEPROM would be write-enabled and its contents might accidently get overwritten when some program would behave in an unexpected manner.

So I'd rather see a "write-enable jumper" on the CFFA card instead of a "write-protect jumper". The EEPROM should only be write-enabled when the jumper is in place and doing its job well.

Your comments, please...

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WP jumper

Postby rich » Thu May 11, 2006 10:38 pm


I tend to agree with your observation. I am not sure why I chose it as I did. You don't have to worry too much about corrosion, as everthing is gold plated.

Actually the change you describe can be done simply by updating the CPLD logic on your board. With the jumper off, the input to the CPLD is going to be pulled to a logic 1, so you would just need to invert the signal in the AHDL code for the CPLD and you would have exactly the change you described.

All you need, in terms of hardware, is a MasterBlaster cable for Altera CPLDs. These are available on e-bay for about US$15.
(NOTE: rev2 CFFA's use an Atmel CPLD now, but they are completely Altera compatible). You will also need a program called: AtmISP to program the parts, and a program called pof2jed to convert the pof file generated by the Altera tools to a jed format for the AtmISP program.
Check the manual and my site for more information on this topic.

Just remember that the CFFA has to be plugged in while you are updating the CPLD logic. Power is not supplied via the JTAG connector.
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