Rev. 1.50, 10/04, page 210 of 448
10.1.5 BF (Branch if False): Branch Instruction
Format Operation Instruction Code Cycle T Bit
BF label If T = 0
PC + 4 + disp × 2 → PC
If T = 1, nop
10001011dddddddd 1 —
Description: This is a conditional branch instruction that references the T bit. The branch is taken
if T = 0, and not taken if T = 1. The branch destination is address (PC + 4 + displacement × 2).
The PC source value is the BF instruction address. As the 8-bit displacement is multiplied by two
after sign-extension, the branch destination can be located in the range from –256 to +254 bytes
from the BF instruction.
Notes: If the branch destination cannot be reached, the branch must be handled by using BF in
combination with a BRA or JMP instruction, for example.
Operation:
BF(int d) /* BF disp */
{
int disp;
if ((d&0x80)==0)
disp = (0x000000FF & d);
else disp = (0xFFFFFF00 | d);
if (T==0)
PC = PC+4+(disp<<1);
else PC += 2;
}
Example:
CLRT ;Normally T = 0
BT TRGET_T ;T = 0, so branch is not taken.
BF TRGET_F ;T = 0, so branch to TRGET_F.
NOP ;
NOP ;
TRGET_F: ;← BF instruction branch destination
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