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PicoBlaze 8-bit Embedded Microcontroller www.xilinx.com 25
UG129 (v1.1.2) June 24, 2008
Processing Data
R
Complement/Invert Register
The PicoBlaze microcontroller does not have a specific instruction to invert individual bits
within register sX. However, the XOR sX,FF instruction performs the equivalent
operation, as shown in Figure 3-2.
Invert or Toggle Bit
The PicoBlaze microcontroller does not have a specific instruction to invert or toggle an
individual bit or bits within a specific register. However, the XOR instruction performs the
equivalent operation. XORing register sX with a bit mask inverts or toggles specific bits, as
shown in Figure 3-3. A ‘1’ in the bit mask inverts or toggles the corresponding bit in
register sX. A ‘0’ in the bit mask leaves the corresponding bit unchanged.
Clear Register
The PicoBlaze microcontroller does not have a specific instruction to clear a specific
register. However, the XOR sX,sX instruction performs the equivalent operation. XORing
register sX with itself clears registers sX and sets the ZERO flag, as shown in Figure 3-4.
The LOAD sX,00 instruction also clears register sX, but it does not affect the ZERO flag, as
shown in Figure 3-5.
Set Bit
The PicoBlaze microcontroller does not have a specific instruction to set an individual bit
or bits within a specific register. However, the OR instruction performs the equivalent
Figure 3-2: Complementing a Register Value
T
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complement:
;
XOR sX, FF invert all bits in register sX, same as one’s complement
LOAD s0, AA ; load register s0 = 10101010
XOR s0, FF ; invert contents s0 = 01010101
Figure 3-3: Inverting an Individual Bit Location
toggle_bit:
; XOR sX, <bit_mask>
XOR s0, 01 ; toggle the least-significant bit in register sX
Figure 3-4: Clearing a Register and Setting the ZERO Flag
Figure 3-5: Clearing a Register without Modifying the ZERO Flag
XOR sX, sX ; clear register sX, set ZERO flag
LOAD sX,00 ; clear register sX, ZERO flag unaffected