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 <[email protected]> > Sent: Sunday, July 9, 2023 4:39 PM > To: General Discussion: On-Topic and Off-Topic Posts > <[email protected]> > Cc: Rob Jarratt <[email protected]> > 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
