UART vs software RS232

[Michael]

I'll try inverting -- that option may be on the module in configuration -- like I say the hardwired connection is fine.

Pardon my lack of knowledge on the matter but what exactly is the difference between
software serin and serout, hserin etc and the UART?

I know the good thing about the UART is that it can run in the background but other than that, what are the differences?

Thanks kindly.

[Normnet]

The USART is hardware, is faster (115.2k baud), has a buffer but is not capable of inverting to eliminate an RS232 driver.

If using SEROUT try inverting or non inverting as per the table in PBP help.

Which command for RS232 are you using?

Norm

[Michael]

By command you mean 8N1?

I'm only using 1200 baud.

So what is Hserin and hserout? I'd still like to know the difference between software generated RS232 and "hardware" RS232.

Just the basics of what is going on.

I'll figure out my problem.....might have to unpack my scope. (wherever it is).

[Normnet]

QUOTE "By command you mean 8N1?"
I mean statement: SEROUT?

Software RS232 can be inverted/non-inverted in software.
Hardware cannot.

SEROUT PORTB.7,1,["START",13] '1200 true
SEROUT PORTB.7,5,["START",13] '1200 inverted

Norm

[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?