Information that may be of interest to HP-75 users posted


When I first got a 75 and started playing with it, I started trying out some of the programs found on the archive diskettes available as lif images on the museum's web site and quickly got frustrated with all the "Error: ROM Missing" messages and to make matters worse there did not seem to be any way to identify what "ROM" was missing A little later I did some reading in the NOMAS for the 75 and figured out was the token was for and external ROM call and found that immediately following the token was the hex LEX number associated with the external call. I then wrote a perl script to go though the lif images and yank out basic 75 files and scan them for external calls. Also from the NOMAS I learned where to look in a LEX file for its LEX number and I built another list of the LEX numbers, names and achhive that contained them, and to that file I added the 'LEX' number for all of the plug in ROMs I have available to me, and then wrote another perl script to merge the two files and the result is a file I call Basic_xref. This file along with the LEX list and a list of keywords from all the LEX files and ROMs I have access to is available on my webspace at Paul's Web Space
the file name is

At the end of March last year there was a brief discussion about a EPROM board for 75s that I was interested in but the seller would not ship to Canada and I was unable to contact him before the auction ended. Through the kind efforts of a gentleman in Australia that was put in touch with the seller, who told me that he was sure he had another one and would look for it for me, well he found it, and I bought it from him. While doing some restoration on the board I rang out all the connections and from that drew a schematic of the board and then later wrote a short description of the circuit, this is also available on my webspace, see link above as 75EPROM.pdf. this exercise has proven very useful as I now have a very good understanding of how the 75 processor accesses memory and how the plug in ROMs work.

I post this in the hopes that some of this will be of some interest and use of others here.


Neat. Thanks.

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