Table of Contents
Advertisement
10.11
BT
Conditional Branch
Format
BT label
Description
This is a conditional branch instruction that references the T bit. The branch is taken if T = 1, and
not taken if T = 0.
The branch destination is address (PC + 4 + displacement × 2). The PC source value is the BT
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 BT instruction.
Notes
If the branch destination cannot be reached, the branch must be handled by using BT in
combination with a BRA or JMP instruction, for example.
Operation
BT(int d)
/* BT disp */
{
int disp;
if ((d&0x80)==0)
disp=(0x000000FF & d);
else disp=(0xFFFFFF00 | d);
if (T==1)
PC=PC+4+(disp<<1);
else PC+=2;
}
Rev. 2.0, 03/99, page 218 of 396
Branch if True
Summary of Operation
If T = 1
PC + 4 + disp × 2 → PC
If T = 0, nop
Branch Instruction
Instruction Code
10001001dddddddd 1
Execution
States
T Bit
—
Advertisement
Table of Contents
