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Intel 8253 - Page 504

Intel 8253
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XA User Guide 6-104 4/17/98
JNB Jump if bit not set
Syntax: JNB bit, rel8
Operation: (PC) <-- (PC) + 4
if (bit) = 0 then
(PC.15-0) <-- (PC + rel8*2); (PC.0) <-- 0
Description: If the specified bit is a zero, program execution jumps at the location of the PC, plus
the specified displacement. If the specified bit is set, the instruction following JB is executed.
The branch range is +254 bytes to -256 bytes, with the limitation that the target address is word
aligned in code memory.
Note: Refer to section 6.3 for details of jump range
Size: Bit
Flags Updated: none
Bytes: 4
Clocks: 10t/6nt
Encoding:
byte 3: lower 8 bits of bit address
byte 4: rel8
1 0 0 1 0 1 1 1
1 0 1 0 0 0 bit: 2

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