|Re: HP-IL RS-232 (a-may-be too-)"techie" questions.|
Message #3 Posted by Eric Smith on 30 Apr 2011, 11:24 p.m.,
in response to message #1 by Diego Diaz
Although the pinout shown in the service manual does match the 8048, I think the actual part must be an 8049 or (less likely) 8050. Those are the variants of the 8048 with more memory.
The 82164 is documented as having a 109 byte receive buffer, 14 4-bit R registers, 12 bytes of C registers, and 4 status bytes. That adds up to 131 bytes, and the 8048 only has 64 bytes of RAM. Even with the 128 bytes of RAM of the 8049, it's a tight squeeze; some of the RAM is taken up by working registers and stack, so some of the 82164A R and/or C register values must be used directly rather than buffered, etc.
I doubt that it's an 8050 because that has 256 bytes of RAM, and they would have been able to make the receive buffer even larger with that part.
Be careful when reading the ROM from an 8048/8049/8050. The verify mode is similar to that of the 8748/8749 EPROM version, but the 8048/8049/8050 should have 12V on the EA pin, vs. 18V for the EPROM version. Without realizing that, I did successfully read an 8049 once on a programmer set for the 8749, but when I tried to do that with another 8049 I damaged the part.