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Repose
Registered: Oct 2010
Posts: 222 |
1670 modem RAM
I've always been curious; a 1670 modem supports the "Hayes command set", meaning it's intelligent and you can type commands to it.
An example is ATS0=100, and ATS0? which set and query RAM location 0. How much RAM is there, and are there spare locations? If so, it would be an interesting way of retaining data between resets, while still powered on.
Another hack of the 1670, is I found it can do at least 1400 baud, if you have a terminal which supports custom rates.
With the 300 baud modem, I believe the 1650, I was able to do 450 baud at least.
If you have two modems, you can connect them directly with a phone cable, no live phone line is needed. It's great for a long wired connection. You can also use a pair of live or dead phone jacks in the same house. The modems will connect even with the dial tone present (although it will make your line busy). North American modular type phone jacks have four wires, and you can get splitters for the second pair, so you could permanently wire two modems together using spare house wiring, without affecting the main (red/green wires) line.
Really curious if someone could test their 1670, using increasing S numbers and matching values to confirm they are independent registers. I also wonder what the fastest (local) baud rate you can talk to the modem is, just being able to send Hayes commands. You can use Novaterm to go pretty high, I think 9600 baud. |
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BiGFooT
Registered: Mar 2002
Posts: 31 |
Check https://www.pagetable.com/?p=1647 |
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Repose
Registered: Oct 2010
Posts: 222 |
Very cool, thanks! Imagine making custom firmware for that, and using it as a co-processor :) |
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Repose
Registered: Oct 2010
Posts: 222 |
2k ROM and 128 bytes RAM. Has swap, DJNZ (like a next), nybble support, basic arithmetic, and 17 registers. It's a bit faster than the C64. A parallel, asynchronous mode would be an interesting addition. Letting it compute XMODEM checksums could be useful too. It could also do the SLIP processing.
http://bitsavers.trailing-edge.com/components/intel/8048/980027.. |
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Martin Piper
Registered: Nov 2007
Posts: 634 |
Are you looking to save and restore data via the user port? |
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Repose
Registered: Oct 2010
Posts: 222 |
I don't need memory, there's better ways to do that, it was just an idea of a fun hack to save some kind of settings which would remain after a hard reset, of course if you don't have a battery backed RAMlink or Quick Brown Box, the only other options I'm aware of. Yes of course you can save to disk, but this would be instant. A good use case: saving the current date. You could remember it between crashes. Or, save a checkpoint when debugging code, then when there's a crash you'd know what function was entered.
The other ideas are what I'd do if I could write a custom firmware for the modem. They would save a lot of CPU time and could give XMODEM ability to dumb terminals.
This idea is used today: we have accelerated ethernet adapters for gamers, which offload TCP processing. |
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chatGPZ
Registered: Dec 2001
Posts: 11116 |
WHat an odd idea :) You could store a few bytes that way, some more or less, depending on how many settings you are willing to clobber. |
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Repose
Registered: Oct 2010
Posts: 222 |
You want to hear a really odd idea? I once had a device driver to use the GUS (Gravis Ultrasound) PC sound card onboard RAM as a disk drive. I think it was only 1MB. |
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oziphantom
Registered: Oct 2014
Posts: 478 |
I was looking to try and reverse the MPS-1250 to find an exploit as that has a 8mhz Mitsubishi M50734SP in it and 8K of ram. Using that a co-processor would be wild it smokes a 1541/1571/1581. |
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Repose
Registered: Oct 2010
Posts: 222 |
That's a really cool idea!
I was also thinking of using the Z80 in the C128 for some subroutines, unfortunately it's no faster than a 6502 for most operations. Then there's the idea of using multiple drives for multiprocessing. |
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oziphantom
Registered: Oct 2014
Posts: 478 |
yeah the 2mhz Z80 is not really that useful, but in cases where you need a lot of registers with prebaked values it can still have some small gains vs the 1mhz 6502 mode. 2mhz 6502 I think just beats it outright. The other trick was the Stack Copy trick however thanks to the MMU the relocatable stack and ZP you can get the 6502 to destroy the z80 stack move with a smallish unrolled loop.
using the drives for co-processor is fine but transfer to and from is slow. To use the 2bit transfer with ATN you can only have 1 drive on the bus. |
