9 Jul
2023
9 Jul
'23
9:12 a.m.
Actually I have just found a more detailed description in the Intel 8080
Microcomputer Systems Users Manual 1975, but it still doesn't tell me
exactly how it works. It isn't completely clear to me if it needs HLDA to be
asserted for I/O W to be asserted.
-----Original Message-----
From: Rob Jarratt via cctalk <cctalk(a)classiccmp.org>
Sent: Sunday, July 9, 2023 4:39 PM
To: General Discussion: On-Topic and Off-Topic Posts
<cctalk(a)classiccmp.org>
Cc: Rob Jarratt <robert.jarratt(a)ntlworld.com>
Subject: [cctalk] VT100: Datasheet for Intel 8228
Hello,
I have a non-functioning VT100. I think I may have isolated the problem to
an
Intel 8228 chip (or 88228, the schematic says 8228,
the part is marked
88228C). Certainly, the part gets a bit hot and it doesn't seem to be
outputting anything on the I/O W pin (pin 27) despite activity on STSTB
(pin
1), DBIN (pin 4) and WR (Pin 3). There is no activity
on the HLDA input
though, but I am not sure if that is required because I think the firmware
is
just trying to send its status to the keyboard LEDs.
I can find a brief datasheet for the 8228 but it doesn't tell me the logic
for
producing the I/O W signal, so I am not sure if it is
behaving as it
should.
Does anyone have more comprehensive information on how
the 8228 is
supposed to work?
I have dumped the ROMs and been able to capture the ROM reads and they
match the disassembled code, so I think the 8080 CPU itself is working.
Thanks
Rob