Computer Hardware User's Guide

Branch Conditionally (Standard) Bcond
13-79 Assembly Language Instructions
Syntax B cond src
Operation If cond is true:
If src is in register-addressing mode (R n , 0 ≤ n ≤ 27),
src → PC.
If src is in PC-relative mode (label or address),
displacement + PC + 1 → PC.
Else, continue
Operands src conditional-branch addressing modes (B):
0 register
1 PC relative
Opcode
31 24 23 16 8 7 015
01101 00
B0 Register or displacement00 cond
Description B cond signifies a standard branch that executes in four cycles. A branch is per-
formed if the condition is true (since a pipeline flush also occurs on a true condi-
tion; see Section 8.2, Pipeline Conflicts , on page 8-4). If the src operand is ex-
pressed in register addressing mode, the contents of the specified register are
loaded into the PC. If the src operand is expressed in PC-relative mode, the
assembler generates a displacement: displacement = label – (PC of branch
instruction + 1). This displacement is stored as a 16-bit signed integer in the
16 LSBs of the branch instruction word. This displacement is added to the PC
of the branch instruction plus 1 to generate the new PC.
The ’C3x provides 20 condition codes that you can use with this instruction
(see Table 13–12 on page 13-30 for a list of condition mnemonics, condition
codes and flags). Condition flags are set on a previous instruction only when
the destination register is one of the extended-precision registers (R7–R0) or
when one of the compare instructions (CMPF, CMPF3, CMPI, CMPI3, TSTB,
or TSTB3) is executed.
Cycles 4
Status Bits LUF Unaffected
LV Unaffected
UF Unaffected
N Unaffected
Z Unaffected
V Unaffected
C Unaffected
OVM Operation is not affected by OVM bit value.
Mode Bit