Faster RS232 port: 115200bps and handshaking, just 5 wires!

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Faster RS232 port: 115200bps and handshaking, just 5 wires!

Postby will » Jan Wed 06, 2010 3:12 pm

I've been playing with my Replica 1. I use it primarily through the serial port, I don't have a keyboard or television connected. I got tired of the slow serial port, dropped characters, figuring out the delay between characters or lines when uploading files, etc.

I've added handshaking between the 6821 and the Propeller chip so it can figure out when the 6502 has consumed each character of input. I've added RTS/CTS handshaking on the serial port and increased the speed to 115,200bps.

No longer is there any need to insert delays between characters or lines, just chuck the file down the serial port and the Propeller delivers each and every character as fast as the system can consume them. No software changes are required on the 6502 -- the original Woz monitor ROM and BASIC etc work exactly as before.

This requires just five additional wires on the Replica 1 board and reprogramming the Propeller microcontroller. Probably takes less than an hour to do.

I wrote the whole thing up:

Let me know how you get on!
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Postby Kallikak » Jan Thu 07, 2010 7:14 am

Nice write up. My Replica is two versions too old to try this, but looks well worth doing on the TE.

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Postby will » Jan Thu 07, 2010 9:16 am

Thanks. I don't have access to the earlier hardware but the CA2 line is present on all 6821s so you should be able to bodge up something similar. You'd have to modify the firmware on the microcontroller (I think it was an Atmel AVR?) to make the same changes I made.

It is certainly a worthwhile mod if you use the serial port.
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Postby vbriel » Jan Fri 08, 2010 2:05 pm

Just a quick note. I've not had time to try this personally, but Will kept in touch with me while running his tests. Something you can do is power up your replica 1 and connect to the PC. Reset the replica 1 so it is up and running. Program the Propeller code into RAM instead of EEPROM. Then you can download your program in 4-5 seconds into the replica 1. If you want Video just press the CLEAR button and that will reset the Propeller back to the original code for the replica 1. You then have your video TV mode back on your replica 1.

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Postby Fippy » Feb Mon 08, 2010 3:58 pm

I've gotten this mod to work and it is incredibly fast and I haven't noticed a single download error yet.

My thanks to Will for his technical support. I had a real problem getting it going at first, and it looks like there might be an issue with the full hardware version of the firmware, which I had been using. Will suggested that I try the RS232 version only, and it worked like a dream, first time.

I'm sure he'll look into that.

Will, I'm willing to reciprocate help. I am happy to try out a future version of your full-hardware version of the firmware, if you need independent validation.

Thanks, Will, for a great mod,
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