The A4/Serial OUT pin - should we keep away from it???

OLDmarty

Senior Member
Hi All,

Regarding the The A4/Serial OUT pin (X2 chips and probably all others?).

I wanted to know *if* i decided to use A4 as an output of some sort, is it likely that my program can lockout the ability for the chip to go back into program mode?
(i *assume* when the chip is in program mode and probably given a higher Vcc voltage it will overide the program running and force programming data handshaking?)

Obviously i would use a 3 pin header to select the A4 pin to connect to either the programmer 'serial OUT' function, or to a control line to an LED, transistor, when the program is normally running...

So, in short, should we use A4?, or should we stay away? ;-)
 

oracacle

Senior Member
I have never personally used it, even with the 28x2 being used for a fair amount of playing around in a few projects (I find its got enough pins without it).
Its serial out so it wont be looking for an input at power up - which IIRC is what causes issues when using serial in on M2 chips as in input. Even with that said I would be tempted not to give it anything to do until things have settled, add in a disconnect.

I wold pause100 >> disconnect or the likes at the start of your code - I put the pause first so that there is a greater chance of the programme interrupt being "caught" before disconnecting

with that you will need to do a hard reset to install a new programme, either with a power removal or hold the reset button until you commence programming.
 

hippy

Technical Support
Staff member
One can use A.4 / Serial Out on the 28X2 as a general purpose output just as C.0 / Serial Out can be used as a general purpose output on the 08M2 etc.

Using the pin should not lock-up the chip when programming; it should reconfigure the output for that when it detects a download initiation. There will be no need for a Hard Reset unless the PICAXE would have required that anyway.
 

Circuit

Senior Member
I have run many projects using the Serial Out pin as an output. In fact, sometimes there is no choice; it has to be used. I find the DAC output very useful for some purposes and this is an obligatory shared output with the Serial Out pin on several of the M2 series. For this application it is important to disconnect the programming cable prior to running the program, simply because the cable messes up the DAC output (...and yes, I did get caught out by that one until I realised what was happening.). Alternatively, as you say, a 3 pin header and jumper can be used to swap the connection.
 
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