Block-transfer instruction
Encyclopedia
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.
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 through TABLE+76 to TABLE+1 through 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
PDP-10
The PDP-10 was a mainframe computer family manufactured by Digital Equipment Corporation from the late 1960s on; the name stands for "Programmed Data Processor model 10". The first model was delivered in 1966...
, the BLT (Block Transfer) instruction copies words from memory
Memory address
A digital computer's memory, more specifically main memory, consists of many memory locations, each having a memory address, a number, analogous to a street address, at which computer programs store and retrieve, machine code or data. Most application programs do not directly read and write to...
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.
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 through TABLE+76 to TABLE+1 through 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
See also
- BitBLT
- Jargon FileJargon FileThe Jargon File is a glossary of computer programmer slang. The original Jargon File was a collection of terms from technical cultures such as the MIT AI Lab, the Stanford AI Lab and others of the old ARPANET AI/LISP/PDP-10 communities, including Bolt, Beranek and Newman, Carnegie Mellon...
entry for: