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

[quote="pjv"]
Guenther;

You are absolutely correct in your assessment.

It also behooves one to realize that on RESET of an SX48/52, that same 5th bit is NOT AFFECTED. So after a reset (not the same as a POWER-UP), the 5th bit may be set, or reset, depending of the previous state.

For greater certainty then, one should only modify the MODE register in an SX48/52 by transferring the content of W through a mov m,w instruction.

Cheers,

Peter (pjv)[/quote]
Yes, true, but under a certain situation, something weird can happen. 

The SX52 data sheet says that M=$0F is only used to READ the port direction registers, and that $1F is used only for WRITES to the direction registers. Refer to the table in the SX52 datasheet (pg 12???). 

Let me clear something up. <B>IN ALL CASES, the M register was = $0F. 

</B>Again, with "mov m,#$0F" the direction registers WILL change. ([b]<b>debugged M = $0F[/b]</b>) 

The dirs WILL NOT change with "mov w,#0F" followed by "mov M,w".([b]<b>debugged M = $0F[/b]</b>) 

The gotcha here isn't the number of bits, it's the $0F value. 

On the SX52 M is supposed to equal $1F to write changes to the direction registers, 

but if bit 5 = 0, and you move literal to M, the direction registers will accept changes. 

Whereas if you move m,w with $0f in w it will not work. 

This is subtle. The gotcha here is that if you port code from an SX28 to a SX52, you may 

have a very difficult bug to find (this is how I discovered it) 

I debugged this several times. You can write direction registers with m = $0f, and you're not 

supposed to be able to do so! 

-Dan

 

P.S. Why does this freaking window double space at random! This double spaced thing is really starting to P!$$ me off!

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