Teletype 43

Ethan Dicks ethan.dicks at
Tue May 23 08:49:21 CDT 2017

On Tue, May 23, 2017 at 12:57 AM, Jim Brain <brain at> wrote:
> On 5/22/2017 8:41 PM, Ethan Dicks via cctalk wrote:
>> Do you have a "traffic light"?  I find them invaluable for diagnosing
>> handshaking and TxD/RxD swaps.
> Yep.  constant low on TX.

Not a positive sign.

> It's entirely possible, but I put a scope on the TX line, and I see no
> activity at all with the unit in DATA or TERM READY mode.  The DATA LED
> blinks, so I think I need to signal the Model 43 that it is "connected".

If it needs hardware handshaking to work, there are a number of
diagrams out there for how to wire the pins together to make the UART
think it's always OK to send.

One example is:

"Connect pins 8 and 7 (i.e. CTS drives RTS)
Connect pins 1, 4, 6 This should maintain the DTR line in the correct
state, by connecting it to DCD and DSR"

It depends on DCE vs DTE and how the vendor wired up their port, but
it's going to be along those lines.

> As has been suggested, I joined GreenKeys and asked if someone has a similar
> setup that works, so I can replicate.


> Worst case is that the driver board has issues, which at least will narrow
> down my search.

Indeed.  It could be the drivers/receivers at the edge of the circuit.
I've had to replace them on occasion when restoring a new-to-me

With a traffic light and an o-scope, it should be easy enough to see
into things - could be cabling, could be a bad IC.  Not seeing TxD
wiggle when you send chars is a pretty fundamental issue.


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