[GreenKeys] Set up RPi for Model 33 Serial Console

[Paul Kasley]

I have not been able to find anything about running an RPi shell on a 33 
so I am posting this to document and disseminate the changes I made to a 
Raspberry Pi to use a Model 33 as a serial console.

My 33 sports a UCC6 intended for interfacing to a minicomputer. I've 
wired the rear terminal strip for full-duplex. The RXD loop current 
measures 12mA. The TXD side is simply normally-closed contacts. I drive 
RXD with a 7400. One side of TXD is pulled up to 5V and the return 
supplies base current to a 2N4401. The RPi GPIO pins accept 3.3V logic 
levels. I do not presently have the reader solenoid interfaced.

The RPi is a model B-plus running Raspian Jessie. These changes will not 
work with Wheezy and I have not tested them with Stretch. The RPi 
translates uppercase input from the TTY to lowercase and LC from the 
shell to UC to the printer.

I have also successfully used the same mods with appropriate changes for 
my Model 40KDP (btw, working printer).

Issues (so far):

1. The round-trip delay to echo from the keyboard through the Pi to the 
printer is annoying. I have an option to loop the keyboard directly to 
the printer but it is disabled unless I can figure out how to get the Pi 
to emit a CR-LF  in response to a CR-only at the end of a command line.

2. Uppercase escape ("\") does not appear to work. There may be a 
difference in the TTY keyboard encoding vs the RPi keyboard layout or 
maybe Jessie just doesn't handle it correctly.

3. These mods are sufficient, but I don't know exactly which are 
necessary. Having the stty at the end of bash.bashrc fixes whatever the 
rest of the OS may have done during startup.

Here goes...

|To use the Model 33 as a serial console for a Raspberry Pi 3:|

|||/boot/cmdline.txt:|

|Replace “||console=serial0,115200”||with “||console=ttyAMA0,110n7”|

|Add ||“loglevel=0”||at the end of the line (suppress kernel messages).|||

||

|/boot/config.txt||:|

|Add at the bottom of the file (grab the UART back from the Bluetooth)
|

|enable_uart=1|

|dtoverlay=pi3-disable-bt|

|||Copy this file:|

|sudo cp /lib/systemd/system/serial-getty at .service 
/etc/systemd/system/serial-getty at ttyAMA0.service|

|||Edit the ExecStart line (autologin gets around UC/LC issues with 
passwords):|

|sudo nano /etc/systemd/system/serial-getty at ttyAMA0.service|

|||ExecStart=-/sbin/agetty –-autologin pi –-noclear 110 %I $TERM|

|||Enable and start the service:|

|sudo systemctl enable serial-getty at ttyAMA0.service|

|sudo systemctl start serial-getty at ttyAMA0.service|

|||At the bottom of /etc/bash.bashrc add:|

|stty –F /dev/ttyAMA0 110 cs7 evenb cstopb –hup iuclc olcuc echo icrnl 
onlcr iexten xcase|

Edit /etc/motd to any text. This will display at log-in:

Teletype Model 33 Demonstration System

Configure eth0 so you can SSH if things get mucked up:

Add to /etc/dhcpcd.conf (use your own address assignments instead of these)

interface eth0

static ip_address=192.168.1.10/24

static routers=192.168.1.1

gateway 192.168.1.1

-Paul Kasley W9TS



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