repairing early HP calcs

Steve Thatcher melamy at
Mon Dec 19 05:07:56 CST 2005

just a note... CPLDs are easier because the EEPROM config is inside the chip (no external hardware and an easy to use interface). The cost of this is available logic density though. You will always get more FGA logic space available then you will with a CPLD. Of course, you can always add more CPLDs, but one FPGA and a 8 pin dip eeprom is less PCB real estate.

best regards, Steve Thatcher

-----Original Message-----
>From: woodelf <bfranchuk at>
>Sent: Dec 19, 2005 2:26 AM
>To: General Discussion at null, On-Topic and Off-Topic Posts <cctalk at>, null at null
>Subject: Re: repairing early HP calcs
>Chris M wrote:
>>I dont own any. But according to a recent Circuit
>>Cellar article, early ics can be easy to implement in
>>a FPGA. Dont have the issue in front of me, but the
>>guy needed to mimic if you will a crt controller.
>>Therefore could the chips used in the early HPs (maybe
>>up to and including the 41 series?) be readily
>>emulated by an FPGA?
>CPLD's are a better part as most FPGA's require pre-load from rom.
>Still you need the original hardware and docs to create a FPGA design.
>Some designers played often some nasty tricks with hardware.
>I think for example in the TRS 80 /I  a 7400 with a defective unused
>gate was used because it was cheaper than a working 7400.

More information about the cctalk mailing list