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Interfacing with a PDP-11/05: Test programs and "Hello, world!"

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Written by: Administrator
Parent Category: How-to's
Category: Interfacing with a PDP-11/05

The serial interface from a programmer's view

The PDP-11/05 has a serial interface compatible with the KL11/DL11 standard.

Here is one excellent additional documentation about a DL11 card.

And this is the register interface in the UNIBUS I/O page, as described in the PDP-11/20 documentation. At 1972, the nomenclature is very paper-tape orientated. Simply translate "Reader" as "Receiver" and "Punch" as "Transmitter".

Register name

Address

Register bits

15-12

11

10

9

8

7

6

5

4

3

2

1

0

TKS = Reader status register

177560

 

RCVR BUSY

 

 

 

RCVR DONE

RCVR INT ENB

 

 

 

 

 

RDR ENB

TKB = Reader buffer register

177562

 

 

 

 

 

RECEIVED DATA BITS

TPS = Punch status register

177564

 

 

 

 

 

XMT RDY

XMIT INT ENB

 

 

 

MAINT

 

 

TPB = Punch buffer register

177566

 

 

 

 

 

TRANSMITTER DATA BUFFER

Name of bits/datafields:

Name of bit field

Function

r/w

RCVR BUSY

1 between the start and the stop bit of an incoming character

read-only

RCVR DONE

1, if an entire character has been received. Starts interrupt if receiver interrupt enable bit is set.

read-only

RCVR INT ENB

receiver interrupt enable bit

r/w

RECEIVED DATA BITS

these bits contain the character just read

read-only

XMT  RDY

Transmitter ready. Cleared when transmit buffer is loaded, set when transmit buffer can accept another character. Will start interrupt if transmitter interrupt is enabled.

read-only

XMIT INT ENB

Transmitter interrupt enable.

r/w

MAINT

Maintenance. When set, the serial line input is connected internally to the serial line output for loopback tests.

r/w

TRANSMITTER DATA BUFFER

A write will start transmission of a character

write-only

 For interrupts, the vector is 000060 for the Reader part, and 000064 for the Punch part. Priority level is BR4.

Serial protocol parameters?

Well, we talked already about the baudrate ... but what about bit length, parity, stop bits?

On other DL11 boards, these values can be set over jumpers. But on the PDP-11/05, there is no choice. The UART is hard wired to 8bit, no parity, 2 stop bits ... the format of paper tapes.

 

Testprogram #1: "Hello, world"

This programs uses and tests only the transmitter.
You have to toggle it in over the blinkenlight console. In the attachement file "hello.blinkenlight_instruction.txt" you find the detailed word-for-word procedure how to enter this program.
Good news: if you have core memory, you have to do this only once.
Start address is 2000.

       1                                
       2                                        .title  Hello world program
       3                                
       4                                        ; This program prints "Hello, world"
       5                                        ; (or any other string) on the serial console at 177650.
       6                                        ; Then it HALTs.
       7                                        ; On CONT, it repeats.
       8                                
       9                                        .asect
      10                                
      11 177560                                 serial = 177560         ; base addr of DL11
      12                                
      13                                
      14 002000                                 .=2000
      15                                
      16                                start:
      17 002000 012702  177564                  mov     #serial+4,r2    ; r0 points to DL11 transmitter section
      18 002004 012701  002032                  mov     #string,r1      ; r1 points to the current character
      19                                nxtchr:
      20 002010 112100                          movb    (r1)+,r0        ; load xmt char
      21 002012 001405                          beq     done            ; string is terminated with 0
      22                                
      23 002014 110062  000002                  movb    r0,2(r2)        ; write char to transmit buffer
      24 002020 105712                  wait:   tstb    (r2)            ; character transmitted?
      25 002022 100376                          bpl     wait            ; no, loop
      26 002024 000771                          br      nxtchr          ; transmit nxt char of string
      27                                
      28 002026 000000                  done:   halt
      29 002030 000763                          br      start
      30                                
      31                                string:
      32 002032    110     145     154          .ascii  /Hello, world/  ; arbitrary text
         002035    154     157     054  
         002040    040     167     157  
         002043    162     154     144  
      33 002046    012     000                  .byte   12,0            ; LF char, end marker
      34                                
      35                                        .end
      35                              

 

Testprogram #2:

This program echoes back any character typed in. Thus it tests receiver and transmitter.
Start address is 1000, so it can coexist with the "Hello world" program above.

       1                                
       2                                        .title  Console serial port
       3                                
       4                                        ; http://www.psych.usyd.edu.au/pdp-11/hints.html
       5                                        ; Any DL-11 style serial port (including the console) can be simply
       6                                        ; tested by depositing 060 (octal) into its 'transmitter buffer ',
       7                                        ; 0777566 in the case of the console. A '0' should appear on the
       8                                        ; console. If it is anything else, check the baud rate settings.
       9                                        ;
      10                                        ; To check the input register, press the '0', then examine the
      11                                        ; receive register 0777562 and it should contain 060.
      12                                        ;
      13                                        ; Needles to say, if you are using any of the Qbus processors,
      14                                        ; or a PDP11/24, /44, /84 or /94 then you need the serial console
      15                                        ; working to do anything.
      16                                        ;
      17                                        ; As simple serial echo test would be:-
      18                                
      19                                        .asect
      20                                
      21 177560                                 kbs = 177560
      22                                
      23                                
      24 001000                                 .=1000
      25                                
      26                                start:
      27 001000 012700  177560                  mov #kbs, r0
      28                                
      29 001004 105710                  wait:   tstb (r0)       ; character received?
      30 001006 100376                          bpl wait        ; no, loop
      31 001010 016060  000002  000006          mov 2(r0),6(r0) ; transmit data
      32                                
      33 001016 000772                          br wait         ; get next character
      34                                
      35                                        ; Note:- PDP11 guru's will notice that I don't test for
      36                                        ; transmitter ready, as there is little point given that you
      37                                        ; cannot type fast enough for it to overrun!
      37                              

consoleserialport.blinkenlight_instructions.txt -- Detailed isntruction how to enter \"Hello\" over panel