DL11-W - UART and new baudrates
After replacing 74LS86 at E27, the baud rate selection logic on the DL11-W has not changed ... you still need good nerves to select a baud rate. There's absolutlely no logic in the switch layout! Here is the new switch-setting-table:
|38400||OFF||OFF||ON||ON||ON||OFF||needs fast UART|
|76800||OFF||ON||OFF||ON||OFF||ON||non-standard and way too fast|
Possible show stopper: the UART
The UART on DL11-W is DEC 19-10459-01. There are a lot of replacement types:
- SMC: COM2017
- AMI: S1883,
- GI: AY-5-1013,
- TI: TMS6011,
- WD: TR1602
Most of these chips can only reach 19200 baud, some even break at ca. 10kBaud.
The AY-5-1013A is capable of 40KBaud and could reach 38400, but is not used on DL11-W.
So bad news are: until you shop, 19200 is the limit.
The good news are: After I replaced my DEC UART (date code 1978) with a AY-5-1013A (1987), 38400 baud are working!
A self test is mandatory, since the 3% speed difference may be intolerable, and the old UART may not be able to communicate well at 19200 or 38400 baud .
Just transmit and receive a lot of characters and check them :-)
You can run one of the DEC diagnostics. "ZDLDI0" on the XXDP2.5 RL02 disk seems to be the best test. A H325 loop back adapter is required.
PDP11GUI is also a good idea:
- Use the "communication self test" function of the "Read/Write disk images windows".
- Choose any non-MSCP disk , click "reset and open disk". A driver is loaded, but no contact to the disk drive is required.
- On the bottom of the window is the self test panel.
- Choose a test strategy ("count up" is fine), and a repeat count (1 is good for the first time) and click "Test". A block of compressed data is sent to the driver and echoed back.
- Since there's parity check in the protocol, you quickly see wether the RS232 port is reliable.