Maxim Integrated MAXQ610 - Manual (Page 49)

3-14
MAXQ610 User’s Guide
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 MAXQ610 microcontroller also supports 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 execution 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