Loop program for the PDP-11

I have used this loop program on both the PDP-11\23 and the 11\34 and assum it will work on just about any PDP useing just the built in ODT code.


1000    005000            CLR R0

1002    12701              MOV #177564 to R1

1004    177564

1006    105711            Loop TSTB R1

1010    100376            BPL Loop

1012    110061            MOVB R0, 2(R1)

1014    2

1016    005200            INC R0

1020    000137            JMP #1006

1022    001006


Use L to load the starting address, D to deposit to that address and E to examine the contents of that address. When your depositing new data in each address you only have to enter the starting address and the ODT will advance to the next memory location on its own, then go back to location 1000 and enter G for go.

Used this little loop on a number of systems and its always fun!

ODT or Console Emulator Functions

In most of the stuff I have played around with the ODT or Console Emulator are built into the Bios of the system, so getting out of the “Boot” prompt dumps you into that system. Remember the emulator only operates in Octal! And all addresses must be even.


L          Load address


E          Examine address


D         Deposits entered data into loaded or examined address


S          Start at loaded address



DL11-W Serial Line Unit Fun and games!


The DL11 Unibus communications card along with any of the Qbus or second source communications cards will always have the same addresses for the input and output register, 777560 for the receiver (Keyboard) and 777566 for the send (display).


By entering “L” 777560 and then “E” you can see the last character sent from the CON keyboard to the system.


By entering “L” 777566 and then “D” you can push that out the transmit buffer and see it displayed on the CON


I know this is stupid but hours can be wasted this way, remember that the numbers in the registers will be in Octal.


YouTube Video of loop on PDP-11/23


YouTube Video of loo on PDP-11/34


Return to " Rays Web Page"


July 13