Hardware handshake on a M8655

[DaveH]

Wanting to transfer reasonable sized text files from my PC to the Lab8 recently and not having one of Philipp,s "magic" USB cards I wandered how hard it would be to add RTS/CTS hand shaking to a M8655. Turns out quite easy.

There is already a driver in place, part of E50 , op on pin 6 to J1 /Y and DD , its input , pins 4 and 5 are strapped to gnd, simply cut the tracks to these pins and feed from the received data available signal, I used E46 pin 9.

There you go, no more overrun, can do a PIP , DTA1:TEST.PA<TTY:/A and when ever the DECTAPE kick's in the data transfer waits. Now iv only tested this at 9600 baud on my " home brew" terminal program but it should work on others, my terminal program automatically adds a CTRL/Z to the end to terminate the transfer, other terminal programs will need this to be done manually.
Dave H

 

[bobaboba]

Aaron Nabil posted along similar lines here: http://pdp-8.org/flow.html but your version seems to be less involved.

 

[AK6DN]

Actually I think DaveH described 'unidirectional' hardware flow control (receive only pacing) whereas the link you provide is for 'bidirectional' flow control (both receive and transmit pacing). Usually the PDP-8 sending to a fast PC won't be a problem, however.

Don

 

[bobaboba]

Yes, looking again I think you're right.

I implemented Aaron's mod on one of my boards while I was getting a machine up because things like Focal take too long between lines too often to do without it. Even Edit couldn't keep up, but the mod worked just fine.

What I usually do now is build anything I need using Simh then use Kyle Owen's os8diskserver to do any transfers to the hardware - iterations are quicker this way.