In SX Microcontrollers, SX/B Compiler and SX-Key Tool, Coriolis wrote:

Well, it seems that noone else will take a stab at you question, so I will try my best. 
 

The documents state that SYNC is related to the turbo mode, looking at the execution pipeline in table 2.7 on page 39 shows that the execution phase of the second instruction occurs during the write phase of the first instruction. During the execution phase of an instruction accessing one of the port registers (reading a port register occurs during the execution phase) if the previous instruction was writing to the same register (/SYNC is off) a race condition may occur, meaning some or all the bits of the write to port instruction may bleed through to the read from port instruction. This presents an unpredictable behavior which can be affected by such things as temperature and processor speed. So to eliminate this nasty behaviour Ubicom incorporated a buffer so that the register the read instruction gets it data from is not the same register as the write instruction is writing to.

 

I may be off on the exact reasoning for /SYNC but I am fairly certain Im at least in the ballpark.

 

Hope this helps,

Paul

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