Block-transfer instruction

On the PDP-10 the BLT (Block Transfer) instruction copies words from memory to memory. The left half of the selected AC specifies the first source address. The right half of the AC specifies the first destination address. The effective address specifies the last destination address. Words are copied, one by one, from the source to the destination, until a word is stored in an address greater than or equal to the effective address of the BLT.

Caution: BLT clobbers the specified AC. Don't use the BLT AC in address calculation for the BLT; results will be random. If source and destination overlap, remember that BLT moves the lowest source word first. If the destination of the BLT includes the BLT AC, then the BLT AC better be the last destination address.

See Also

• BitBLT
• Jargon File entry for:
  • BLT
  • blit
  • bitblit

Programming examples

Save all the accumulators:

       MOVEM   17,SAVAC+17
       MOVEI   17,SAVAC        ;Source is 0, destination is SAVAC
       BLT     17,SAVAC+16

Restore all the accumulators:

       MOVSI   17,SAVAC        ;Source is SAVAC, destination is 0
       BLT     17,17

Zero 100 words starting at TABLE.

       SETZM   TABLE
       MOVE    AC,[TABLE,,TABLE+1]     ;Source and destination overlap
       BLT     AC,TABLE+77

Move 77 words from TABLE thru TABLE+76 to TABLE+1 thru TABLE+77. BLT can't be done here because the source and destination overlap.

       MOVE    AC,[400076,,TABLE+76]
       POP     AC,1(AC)        ;Store TABLE+76 into TABLE+77, etc.
       JUMPL   AC,.-1

References

• MIT PDP-10 'info' file