rodsmallwood52 at btinternet.com
Sat Dec 8 01:10:44 CST 2018
I’m sure that would work but I only have an 8650 110 baud only card
Sent from Mail for Windows 110 baud
From: Bob Rosenbloom via cctalk
Sent: 08 December 2018 03:41
To: cctalk at classiccmp.org
Subject: Re: PDP-8/e
On 12/7/2018 7:01 PM, Pete Turnbull via cctalk wrote:
> On 07/12/2018 17:44, Jon Elson via cctalk wrote:
>> On 12/07/2018 11:22 AM, systems_glitch via cctalk wrote:
>>> Indeed, unless you need character pacing.
>> Actually, with the correct settings of the serial port (xon/xoff or
>> CTS pin) the serial port driver should do this, too, so cat would work.
> A PDP-8/E doesn't have a CTS pin and the loaders don't support
> XON/XOFF, though.
The PDP-8 needs to control the serial CTS function. This was called
reader-run when using a Teletype machine. FOCAL won't load without it.
You can modify the serial card (mine was an M8655) to support the
function. Here's what I did:
Cleaned up from Aaron Nabil's and Lyle Bickley's write up.
Hack the M8655 to support reader-run by mapping it to RS-232 hardware
1. Cut the trace leading from Pin 1 of E54 (a 7400). This is the input
that clears the Reader Run FF when a new character starts to come in.
2. Jumper from Pin 1/E54 to Pin 3/E38, a spare gate on a 7400 that we
are going to use an inverter.
3. Tie Pin 1 and Pin 2 of E38 together, and run them to Pin 20 of E19,
This supplies the signal to the reader-run FF that tells it that
it's got an incoming character and to de-assert the reader-run line.
Normally this is tied to the current loop receiver, we've just
moved it to the UART so any received data will clear the FF.
4. Cut a ground traces on 4 of E50, a 1488 RS-232 transmitter. This is
what would normally supply the continuously asserted RTS (and DTR) signal.
5. Jumper from pin 7 of E39, a 7474 flip-flop to pins 4 of E50. E39 is
the "reader-run flip-flop". Now RTS follows the reader run signal.
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