Just a quick update on this. I have a BBS (Synchronet) running enough that I can dial-in from another PC and connect properly. I started with the Hayesmodem 300, which was painful, and then changed to the Hayes Optima 144 which was respectable for dial-up.

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Using the Z80MC, I can get the modem to go off-hook, dial, and connect but it’s not sending/receiving. I use this same modem with HyperTerm to dial the BBS, so it’s not the modem or cable. I’m thinking it’s related to handshaking so I need to look at the init string.?I might also try the following: switch to 32K SRAM and lift the RTS/CTS pins on the 8250 and bring them out to the level shifter DE9 that I have and see if that makes a difference – it would provide full handshaking.

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Even with that, overall, good progress in getting it going. More to come once I get the 32K SRAM next week.

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Good point. I think I have a 512K one because that’s what I had handy – they’re used in many of the Retrobrew ECB and John Monahan’s S100 various boards. I don’t think I have any 62256 chips around, but so long as I keep handshaking disabled, we should be good.

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I will give a revised ROM a try. It’s just an extra set of steps to use, but might be a fair compromise given the very narrow use for this.

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I requested a full data sheet on the modem from the manufacturer. It uses the AT command set which is good, but it has a reset pin, so I’m looking for the required pulse width for it. RESET isn’t exposed on the Z80MC when it’s in a case – P1 on the SIO has a missing “key” pin with no hole. So, I plan on a simple RC circuit local to the modem (if needed).

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I found a text-based browser called “Links” which is like Lynx but it seems to be pure text with no DOS-graphic characters. It’s written in C, so maybe there’s a way to pare it down to a bare minimum just to parse basic HTML. Need to look at that.

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More to come!

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