UART vs software RS232

[Archangel]

QUOTE

SEROUT PORTB.7,<font color=red>1</font color>,["START",13] '1200 true
SEROUT PORTB.7,<font color=red>5</font color>,["START",13] '1200 inverted

Norm

RTFM applies here, in the serout and serout2 sections, you will discover " MODE ", now when using <font color=red>SEROUT</font color>, if you <font color=blue>INCLUDE "modedefs.bas"</font color>, you can specify the mode as in below:

SEROUT PORTB.7,<font color=red>T1200</font color>,["START",13]  '1200 true
SEROUT PORTB.7,<font color=red>N1200</font color>,["START",13]  '1200 inverted

[BrianT]

RS-232 defines the idle condition as steady MARK. This is -3 to -15 volts AT THE CONNECTOR. Likewise SPACE is a positive voltage of +3 to +15 AT THE CONNECTOR. In contrast, PIC 'idle' is almost always assumed to be 0 volts.

These high(ish) interface voltages are well beyond TTL levels and so an Interface Converter or Line Driver is frequently required such as the older 1488 and 1489 or the newer MAX-232 family. Line Driver chips also serve for electrical protection of the PIC from outside interference and are usualy socketed on the circuit baord for easy replacement as they get zapped fairly often.

Line drivers/interface converters are all INVERTERS. So this means the levels at the PIC are now the opposite of what you mention in your first post. MARK, which was a negative voltage at the connector becomes +5 volts at the PIC. SPACE becomes 0 volts at the PIC.

SERIN allows selection of 'true' and 'inverted'. You use 'true' when you use a line driver or max-232, otherwise use the 'inverted' setting when you have no interface chip in line. HSERIN and SERIN2 expect you to use an inverting interface chip IF you are going to the outside world via an RS-232 connector.

For short distance or internal PIC to PIC comms you can dispense with the line drivers but you will probably get errors in the first character when sending between PICs at TTL levels.

To eliminate these errors all you have to do is condition the interface to 'mark' with a positive voltage long enough for a character time. You only need do this at the start of each message or you can ignore this issue and simply add a few throwaway characters at the start of every message. I find it better to add the HIGH xxx : PAUSE n and get every character every time.

Try using
HIGH TxDpin
PAUSE 1
and then output your message such as..
SEROUT/HSEROUT/SEROUT2 TxDpin, message

HTH
BrianT

[Michael]

I know all about the history of those higher voltages but now in the 0 - 5 volt world....does it really just come down to this?....

HSEROUT and HSERIN needs an inverted input where SEROUT and SERIN can operate either true or inverted? (as long as both ends are the same?)

My device is set to true, 1200 baud, 8N1....having problems with wireless but fine with wired...whether a straight short RS232 or I also have an RS485 connection that can run for a mile. Works like a champ.

I'm going to look closer at it today -- never had much luck with wireless.....(yet).

Fact is though, using serout and serin, phase isn't an issue, as long as both ends are the same, right? Both T or Both N.

Correct?

[Normnet]

What is the RS232 spec on the device to which you are interfacing?

Norm

[Michael]

I'm not having any luck -- works great wired though.

As mentioned before, I'm using the PIC (16c65b) SEROUT and SERIN.

The wireless device is a maxstream Xstream X24009 oem module.

The interface listed in the data sheet says CMOS UART (as I mentioned before).

I've tried everything.

Inverting one side, both sides, putting the signals through a 4011 inverter....the scope shows
data on the rcvr and xmtr but I don't have a dual trace so it's really hard to see how the streams are matching up.

Oh well -- I went through this before, I may just give up and move on.

I wish I would have used the PIC's hardware UART in the first place....too late now.

[Bruce]

I have a pair of XStream units I've been using for a few years that work great. Just use
true mode and connect PIC I/O-pins directly to them.

It may be that you have them configured for another data-rate or something, but I would
check with Digi or Maxstream to be sure they're working if having problems with them.

Mine worked perfectly right out of the box.

[earltyso]

For what its worth, I use LINX RXM/TXM-XXX-LR serial modules with inverted 9600 8N1 with no problems at all. I use serin/serout2 commands and just played with my timing to be able to update both my reciever boards with string data. The serial modules work GREAT up to 3000' away and can go up to 10k baud. I would give them a shot if you are frustrated with the other modules you are using. The price for the pair ~ 25.00 so not too bad. You can also purchase the development board.

Here is one line of code using 8N1 9600 inverted

SERIN2 PORTB.0,16468,[WAIT("TENSION"),DEC4 TN]'TEST 3

good luck!