BS2 simple serial out works with any pin but not Pin1 - Sout

NY2KW

I need all digital pins P0-P15 for my project. I also need to send a data stream (one direction) to a PIC device. I am using the following basic code to send a test stream. The PIC expects True polarity not inverted:

' {$STAMP BS2}
' {$PBASIC 2.5}
' {$PORT COM12}

Main:
DO
SEROUT 16, 396, ["Hello!", CR] ' send the greeting
PAUSE 100 ' wait 0.1 seconds
LOOP ' repeat forever
END

It doesn't work on Pin 1 however it works fine if I change SEROUT to any other pin.

Just to be sure I looked at the Pin output on my scope which has a UART logic decoder and its all gibberish regardless of settings I try. With the BS2 set for any pin 0-15, the code works perfectly and my scope easily decodes.

Would the line driver on Pin Sout be affecting this? The only wires I have from BS2 to PIC (or scope) are the Sout and Ground.

Any advice appreciated.

Jerry NY2KW

Phil Pilgrim (PhiPi)

You realize that the RS232 driver on PIN 1 inverts the signal, right? Try 16780 instead of 396 to re-invert it.

-Phil

NY2KW

Yes, thanks. I dont seem to be able to change the signal polarity. The signal pattern looks identical on my scope with either

SEROUT 16, 396, [string]

or

SEROUT 16, 16780, [string].

My scope to decode does not automatically find the right polarity - i have to set it and I leave it unchanged with both 396 or 16780 and the signal burst is identical.

Any suggestions?

TIA
Jerry

Phil Pilgrim (PhiPi)

Just checked, and you're right: the signal does not get inverted with 16780 like you might expect on P16. Soooo ... it looks like you'll have to add an external inverter.

-Phil

Tracy Allen

The serout inverter on the BS2 is a single PNP prebiased transistor you can find on top of the BS2 module. You could tap/hack into the base of that transistor to find the non-inverted signal.

Another peculiarity of the Stamp wiring is that the collector of that PNP transistor is connected both to pin 1 of the module, SOUT, and to a 4.7kohm resistor that goes to the SIN pin. The idea is that SOUT will "steal" negative or zero voltage from the SIN pin. If SIN is floating, there is still a path to ground via a pair of 10k resistors and the base of the NPN transistor that inverts the SIN signal. You can see the schematics in the appendix of the Stamp manual.