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Reading / Writing the Atari 400 / 800 serial port?

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My 810 does not seem to be working. It is the only serial device I have. I want to write a program to send data to the serial out to see if it is ny 810 or the serail port on the 800 that is the issue.


I wrote a RS232 driver for a custom RS232 interface I designed but that was 30 years ago. And of course the code is on the disk so I can't get to it.



Can anyone point me to some sample code for talking to the SIO? I just want to send raw data out.


Or can someone remind me, do I want to look at the pokey interface or the CIO interface?

Edited by spinnaker15136

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In the back of my OS manual, I have some cryptic notes scribbled:


With 3&4 Clock


399 baud = 11-high 163-164-165 LOW

53766 53764



2976 circled


I am sure I knew what that meant at the time. I sure wish I took better notes. ;)


53766 is the Audio channel 4 frequency and 53764 is channel 3 frequency.




So I am guessing maybe I wrote directly to the registers for my driver to at least set up the baud rate.


I wrote some basic code to do noting but write to 53773 (serial out but I saw no transitions on the serial port.

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I found this on my hard disk to send something to the serial port:

99 REM 01-JAN-2000
100 OPEN #1,13,0,"R1:"
110 XIO 36,#1,14,0,"R1:"
120 PRINT #1,"NEUES HALLO!";CHR$(13);CHR$(10)
130 CLOSE #1

It opens the port with 9600 baud (XIO "14" parameter), 8n1. Although the open specifies input+output (parameter "13" in OPEN), it doesn't start concurrent I/O. But I guess it worked, otherwise I wouldn't have kept it or fixed it to work. For input you have to start "concurrent mode" with XIO 40. See the 850 user's manual for more information.




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My opinion only and by experience you might want to

replace your 6520 on the 800 with a 68B21 since I've

had two out of three 800s that needed that done to

it before any device answered to a SIO call. Reseating

the chip may help too, but in my case the 6520 was

nonfunctional with repeated attempts AFTER I got a

good 68B21 in there. For some reason the early 6520s

weren't made to last?


Others should be in here going on about a new Pokey,

can't fathom where they are, but both 40 pin chips

have been found to be lacking after a 30 year nap.


I'm not kidding 2 out of three, needed a new 68B21

which is identical to original 2 MHz 6520 PIA. eBay


signals directly while Pokey creates Data and Clock



It's also important to spray some contact cleaner of

the de-oxit type on the drive select switches and

while still wet, work them quite well. And again

after drying. I need to do this every ten years, the

state they relate to the drive's OS comes and goes

such that the drive really doesn't know which one it

is at any random moment and will only boot from Drive

1 anyway.

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