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M1 2 chip Level II ROM (no 3 chip expansion board) ???

neusse

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Joined
Oct 16, 2022
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Hello Everyone. I dug out my old M1. Bought it when I was 17 a million years ago. It still powers up, but I get garbage on the screen. That is not what I am writing about.
I dont remember if I bought it with Level II basic or not. But It does have Level II basic in it. But only on 2 Rom chips. No expansion board is installed. I am confused I cannot find any information on what this is and why only 2 chips and not 3.
I removed the roms and read them out. Not sure what version it is but they do have the text Level II basic in the dump.
The other strange thing is one of the Roms has been bodged. VCC is jumped over to A11 and A11 is clipped so it does not plug into the socket any longer???

Has anyone ever seen this?

oh and these chips seem to be 2732 equivalents.


hmm. The date codes (8043) seem to indicate I upgraded to level II basic 2 or 3 years after I bought the M1. Very long time ago. I don't remember. So maybe this was some trick upgrade someone did for me?

Any thoughts are welcome.




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The date codes are the "947" and "948" (November 1979) (for some reason, NEC could only afford 3-digit date codes). The "8043364" and "8043732" are the part numbers, in which the "64" and "32" reflect the number of kibibits (thus, there are 12 kibibytes total). The pinouts follow the Motorola MCM68A364 and MCM68A332, in which pin 21 is A12 on the '64 and one of the chip selects on the '32.

There were two 2-chip Level II BASIC ROM sets: you have one of the last of the 8043364/8043732 sets, which started production in early 1979. The other set was 8044364/8044732, which started production in around January 1980.

I can't say for sure whether I've seen that modification, but it wouldn't surprise me if that's exactly what Radio Shack techs were instructed to do to get this particular ROM set to work with whatever particular board revision you have. (The service manual for the Level II BASIC ROM upgrade is one of the few service manuals I've never seen any trace of online.)
 
The satellite board was not needed for the Rev G Model I CPU board, so that is likely what you have.
 
neusse, they seem to be LEVEL II ROM v1.2 that was released around July 1979 through July 1980. It displays the "MEMORY SIZE?" prompt not the "MEM SIZE?", right? Also it has the fixes for the floating point compare routine and the DATA/READ pointer random repositioning to the start of DATA. Hope this sheds some more light to your ROMs. Jim
 
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