Computer Hardware User's Guide

SUBC Subtract Integer Conditionally
13-226
Syntax SUBC src, dst
Operation If ( dst – src ≥ 0):
(
dst – src << 1) OR 1 → dst
Else:
dst << 1 → dst
Operands src general addressing modes (G):
0 0 register (R n , 0 ≤ n ≤ 27)
0 1 direct
1 0 indirect (disp = 0–255, IR0, IR1)
1 1 immediate
dst register (R n , 0 ≤ n ≤ 27)
Opcode
31 24 23 16 8 7 015
00 0 10 1
1 01
dst
G
src
Description The src operand is subtracted from the dst operand. The dst operand is loaded
with a value dependent on the result of the subtraction. If ( dst – src ) is greater
than or equal to 0, then ( dst – src) is left-shifted one bit, the least significant
bit is set to 1, and the result is loaded into the
dst register. If ( dst – src ) is less
than 0, dst is left-shifted one bit and loaded into the dst register. The dst and
src operands are assumed to be unsigned integers.
You can use SUBC to perform a single step of a multi-bit integer division. See
the TMS320C3x General Purpose Applications Guide for a detailed descrip-
tion.
Cycles 1
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