Inverted baud setting for serial out versus not inverted

Buck Rogers

Hello!
I have a BS2 configured to deliver serial data to logic using these instructions:

' {$STAMP BS2}
' {$PBASIC 2.5}
X VAR Byte
OUTPUT 0
OUTPUT 1
OUTPUT 2
OUTPUT 3
FOR X = 65 TO 91
SEROUT 2, 84, [X]
SEROUT 4, 84, [X]
'DEBUG HEX X,CR
DEBUG DEC X,CR
PAUSE 1375
NEXT
HIGH 0
HIGH 1
HIGH 2
HIGH 3

The connection to P2 is going off to a part that eventually sends its output to a (now obsoleted and discontinued) DS275. According to an earlier discussion, that particular device requires that the instruction

SEROUT 2, 84, [X]

be fed a baud rate that's inverted.

I am wondering why is that necessary. The device is then connected to a Palm IIIe running the PalmOrb software from http://palmorb.sf.net that program for the Palm was originally written to emulate an expensive display. Which is the Matrix Orbital LK204-25 LCD. That website is still complaining that it needs a maintainer by the way. (The program not the site.)

If anyone wishes to examine a photo of what's at work, please feel free to ask. A schematic of it, is possible but creating one is a bit of a difficult proposition.

Mike Green

Without documentation on the device involved and on the circuit, it's impossible to say for sure why the device might require an inverted signal level. One reason for this sort of thing is that the device may be designed for connection to an RS232 signal which is normally considered to be inverted. Since the Stamps don't produce RS232 voltages, your device probably is RS232 compatible, but is tolerant to 5V logic voltages. In any event, if the device is supposed to use inverted signal levels, use an appropriate Baud code (see the Stamp Manual for those).

Buck Rogers

Mike Green wrote: »

Without documentation on the device involved and on the circuit, it's impossible to say for sure why the device might require an inverted signal level. One reason for this sort of thing is that the device may be designed for connection to an RS232 signal which is normally considered to be inverted. Since the Stamps don't produce RS232 voltages, your device probably is RS232 compatible, but is tolerant to 5V logic voltages. In any event, if the device is supposed to use inverted signal levels, use an appropriate Baud code (see the Stamp Manual for those).

Hello!
Excellent point. I'll provide the documentation for the DS275. Now regarding the circuit, that's a poser. If necessary I'll present the schematic and perhaps a photo RSN, but only if necessary. Okay the documentation is now attached. Circuit and stuff.... Well only if you (or the next reader) feels it would be needed. Did you by chance visit the website for the application running on the Palm?

PJAllen

That DS275 operates just like a MAX232/233.
TXout and RXin are RS232 signalling.
TXin and RXout are TTL/5V.

Mike Green

The way forums like this work is that you provide the raw material for your question and state your question as clearly and concisely as possible. Obvious beginners are usually forgiven and guided into how to do basic research and the exchange of information. The mostly volunteer "experts" try to take the information provided, extract relevant details, and guide the questioner into finding the answer they want. In the process, ideally, others who might be lurking or who might find the thread in the future hopefully will also learn something. If your question is not well stated or you leave out possibly important information, it will either increase the amount of work required by people who volunteer their time and energy or it will result in getting very general and maybe not applicable or useful advice (to you for your specific problem) or both.

I did eventually visit the link for the Palm software. There was nothing there that really changed my previous answer.

Buck Rogers

Mike Green wrote: »

The way forums like this work is that you provide the raw material for your question and state your question as clearly and concisely as possible. Obvious beginners are usually forgiven and guided into how to do basic research and the exchange of information. The mostly volunteer "experts" try to take the information provided, extract relevant details, and guide the questioner into finding the answer they want. In the process, ideally, others who might be lurking or who might find the thread in the future hopefully will also learn something. If your question is not well stated or you leave out possibly important information, it will either increase the amount of work required by people who volunteer their time and energy or it will result in getting very general and maybe not applicable or useful advice (to you for your specific problem) or both.

I did eventually visit the link for the Palm software. There was nothing there that really changed my previous answer.

Hello!
I see.
Given the time of day when I posted the original, it was either very early in the morning my time, (or also very late at night), I might have missed stating the obvious because of sleep deprivation. Further testing after I provided a copy of the data sheet, for which PJ Allen confirmed most of my theories, and as it happens means that I can now mark this as solved. Having done that, I'm also going to keep working with it. And swap the normal for inverted baud setting.

Mike Green

Glad things are working out. Being sleep deprived does take its toll. There's a limit on what coffee or strong tea can solve.