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TRS-80 Model 1 RS-232 data rates

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Hi all, 


I've had a Model 1 for a few months now and have been enjoying learning about it.  I was always an Atari guy growing up so I wasn't a fan of TRS-80s back in the day, but now that I have one I'm really enjoying and appreciating it.  My machine came with an Expansion Interface that happily also contained a serial card, Radio Shack model 26-1145. This appears to be by far the most common RS-232 interface for the machine. I purchased a serial cable from Ian in Australia recently, so I'm just now getting some experience with TRS-80 RS-232 communications. 


My question is around what my expectations should be for maximum data rates.  The RS-232 board supports 9600 baud and the DIP switches are set that way.  However when I connect the machine to a WiFi modem with a DTE rate of 9600, it drops characters like mad.  Even if I drop the DTE rate to 2400 baud I still lose some characters.  The modem is set for hardware handshaking but I have no idea whether the interface even supports that. 


I'm not at all what the best/fastest terminal software is, whether I need modify the cable so that I'm supporting RTS/CTS/DTR etc, and so on.  Anyone who can share a bit of experience with these machines as terminals would be very helpful!


Thanks for any guidance...

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  • 2 weeks later...

Just wondering people do in other parts of atariage and I saw your post.


I could be that TRS80 expects hardware handshake to be respected by the sending side so transmission stops when TRS80 is putting data into memory.


You might make some progress by setting up an RS232 on a PC and send text files to the TRS80 with TeraTerm and change the handshake options

to see what your Tandy software responds to. It sounds like the software is not using an interrupt on the receive side but rather is polling RS232 with software.

That is always a problem for high-speed receive. 


I have spent way to many hours debugging RS232 30 years ago. :) 


Not very helpful but it's all I got. 

Best of luck. 



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Thanks for the suggestions. I think you’re right, I need to connect something that’s a bit more of a known quantity to the TRS-80 and test further. Also time to pull the old breakout box out of storage so I can monitor the signals.

I did quite a bit of research on this question over the last week or so and one of the things I learned is that all I/O devices on the system are mapped to specific memory locations (common for 8-bit) and the the TRS-80’s serial interface has specific bits in the serial port block that map to DSR and CTS (received signals from DCE) and DTR and RTS (transmitted signals). So, hardware handshaking is definitely possible if the terminal software on both ends knows how to do it. 

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