Maxim-integrated MAXQ622 Bedienungsanleitung PDF herunterladen (Seite 50)

MAXQ612/MAXQ622 User’s Guide

3-14 Maxim Integrated

When the supplied loop address is outside the relative jump range, the prefix register (PFX[0]) is used to supply the

high byte of the loop address as required.

move LC[1], #10h ; loop 16 times

LoopTop: ; loop addr not relative to djnz LC[n],src

call LoopSub

...

djnz LC[1], LoopTop ; decrement LC[1] and jump if nonzero

; assembles to: move PFX[0], #high(LoopTop)

; djnz LC[1], #low(LoopTop)

If loop execution speed is critical and a relative jump cannot be used, one might consider preloading an internal 16-bit

register with the src loop address for the “DJNZ LC[n], src” loop. This ensures that the prefix register does not need to

supply the loop address and always yields the fastest execution of the DJNZ instruction.

move LC[0], #LoopTop ; using LC[0] as address holding register

; assembles to: move PFX[0], #high(LoopTop)

; move LC[0], #low(LoopTop)

move LC[1], #10h ; loop 16 times

...

LoopTop: ; loop address not relative to djnz LC[n],src

call LoopSub

...

djnz LC[1], LC[0] ; decrement LC[1] and jump if nonzero

If opting to preload the loop address to an internal 16-bit register, the most time and code efficient means is by per-

forming the load in the instruction just prior to the top of the loop:

move LC[1], #10h ; Set loop counter to 16

move LC[0], IP ; Set loop address to the next address

LoopTop: ; loop addr not relative to djnz LC[n],src

...

3.7.6 Conditional Returns

Similar to the conditional jumps, the MAXQ612/MAXQ622 microcontrollers also support a set of conditional return

operations. Based upon the value of one of the status flags, the CPU can conditionally pop the stack and begin execu-

tion at the address popped from the stack. If the condition is not true, the conditional return instruction does not pop

the stack and does not change the instruction pointer. The following conditional return operations are supported:

RET C ; if C=1, a RET is executed

RET NC ; if C=0, a RET is executed

RET Z ; if Z=1 (Acc=00h), a RET is executed

RET NZ ; if Z=0 (Acc<>00h), a RET is executed

RET S ; if S=1, a RET is executed

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Maxim-integrated MAXQ622 Bedienungsanleitung Seite 50