DL11-W - UART and new baudrates

Parent Category: How-to's Category: Faster baudrates for DL11-W Written by Administrator

Selecting 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: 

Baudrate Transmit Receive Info
  S4-10 S3-1 S3-4 S3-2 S3-3 S3-5  
110 ON ON ON OFF OFF OFF  
1200 OFF ON ON ON OFF OFF  
2400 ON OFF OFF OFF ON ON  
4800 ON OFF ON OFF ON OFF  
9600 ON ON OFF OFF OFF ON  
19200 OFF OFF OFF ON ON ON  
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!

replaced uart

 

Test

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:

  1. Use the "communication self test" function of the "Read/Write disk images windows".
  2. Choose any non-MSCP disk , click "reset and open disk". A driver is loaded, but no contact to the disk drive is required.
  3. On the bottom of the window is the self test panel.
  4. 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.
  5. Since there's parity check in the protocol, you quickly see wether the RS232 port is reliable.