1989_MELPS_7700_Software_Manual

BBC Branch on Bit Clear BBC
Operation
When M 1\ IMM=O
PC f- PC + n ± REL (REL is instruction's second byte)
PG f- PG + 1 (if carry on PC), PG f- PG - 1 (if borrow on PC)
When M 1\ IMM""O
PC f- PC + n
PG f- PG + 1 (if carry on PC)
IMM is the bit pattern that specifies the bit positions to be tested.
The value of n is determined as follows:
If the data length selection flag m is set to 1, n=4 if direct bit relative
addressing mode, and n=5 if absolute bit relative addressing mode.
If the data length selection flag m is set to 0, n=5 if direct bit relative
addressing mode, and n=6 if absolute bit relative addressing mode.
Description
The SSC instruction tests the specified bits (which may be specified simultaneously)
of memory. The instruction causes a branch to the specified address
when the specified bits are all O. The branch address is specified by a relative
address.
Status flags
Not affected.
Addressing mode Syntax Machine code Bytes I Cycles
Direct bit relative BBC #imm, dd, rr 3416, dd, imm, rr 4
Absolute bit relative BBC #imm, mmll, rr 3C16, II, mm, imm, rr 5
(Notet) The bytes-count increases by t when operating on t6-bit data with the data length selection flag
m set to O.
(Note2) The cycles-count increases by 2 when a branch occurs.
I ~
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