VT-320 interfacing

Grant Taylor cctalk at gtaylor.tnetconsulting.net
Mon Nov 9 19:53:57 CST 2020

On 11/9/20 5:36 PM, Joe Piche via cctalk wrote:
> Hi All.


> The VT320 only has the DEC-423 MMJ, no RS-232.

I /thought/ that Modified Modular Jack was simply a physical thing and 
completely independent of Recommended Standard 232.

Every MMJ that I've run into has had RS-232 run through it perfectly fine.

> I found a number of guides that show how to wire up the DEC-423 
> connector to a DB-9 RS-232, but so far I have struck out. It will 
> receive text from the remote computer, but I do not see anything on the 
> remote when I type on the VT-320.

Can you enable local-echo on the VT-320?  If you can, do you see 
anything appear there when you type?

> I have loop backed the TX to RX on the VT-320 terminal, and it does 
> work. TX=RX Baud rate  in the VT320 settings, and the data bits, parity, 
> & stop bits match.

What, if any flow control is in use?

> DEC-423 (lock tab bottom right, pin one on the left, 6 on the right)
> 1    DTR
> 2    TXD
> 3    TXD-
> 4    RXD-
> 5    RXD
> 6    DSR
> For a cross over cable:
> 423 #2 goes to DB9 #2 (TX to RX)
> 423 #3 & #4 to DB9 #5 (TXD- and RXD- to GND)
> 423 #5 goes to DB9 #3 (RX to TX)
> 423 #1 to DB9 #6 (DTR to DSR)
> 423 #6 to DB9 #4 (DSR to DTR)
> Does this look like it should work? It does leave DB9 RTS and CTS 
> unconnected.

That would likely be a problem for hardware flow control.

> Thanks!

Good luck.

Grant. . . .
unix || die

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