Proper syntax for #use rs232 function

jlucas · Joined: 08 May 2011 Posts: 41 Location: Carthage, MO

This question is so simple that it seems no one has even had to ask it before. I'm trying to send 8-bit data from a PIC 18F4520 to a Laird/Aerocomm AC4790 RF transceiver module at 57,600 baud. The default state of both the send and receive pins is HIGH. The AC4790 module requires a low start bit, then 8 data bits, then a low stop bit. It sounds pretty straightforward, but I've searched the forum for about 3 hours, and I can't find the answer.

If I had designed this function, what I want to do would look like this:

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

jlucas · Joined: 08 May 2011 Posts: 41 Location: Carthage, MO

Thanks for the quick response. This sounds almost too good to be true, but I'll certainly give it a try! Very Happy

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temtronic · Posted: Mon May 09, 2011 5:29 am

Also be aware that USE RS232(...) requires a MAX232 or equal by default.

And.. add the 'errors' option to it as well.

SherpaDoug · Joined: 07 Sep 2003 Posts: 1640 Location: Cape Cod Mass USA

If you use a software UART there is the "invert" option.
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PCM programmer · Joined: 06 Sep 2003 Posts: 21708

The AC4790 chip uses a direct, non-inverted, TTL-level connection to the PIC.
It doesn't need a Max232 chip and he doesn't need the INVERT option.

http://www.lairdtech.com/Products/Wireless-M2M-and-Telematics-Solutions/Proprietary-Radio-Modules/DataSheets/AC4790-0209/

http://www.lairdtech.com/DownloadAsset.aspx?id=2548

Also, he is using a software UART (since he's using pins D4 and C2) so
the ERRORS directive doesn't do anything. It's ignored by the compiler.

He didn't give the exact dash number of the AC4790 that he's using, and
different versions can run at 5v or 3.3v. So depending upon the Vdd
voltage of the PIC, he could have an issue with the logic voltage levels.

jlucas · Joined: 08 May 2011 Posts: 41 Location: Carthage, MO

Oops! I made a mistake in my post. The start bit is low, but the stop bit is high. If a low stop bit is the default, does that mean I need this?

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

CCS uses the standard signaling methods. The AC4790 expects the
standard methods. You don't have to do anything.

Also, look on page 18 of the AC4790 manual. It shows the Stop bit is
at a high level, which is the standard.

And "Stop=1" just tells the PIC to transmit 1 Stop bit (it could be set to
send 2 stop bits).

jlucas · Joined: 08 May 2011 Posts: 41 Location: Carthage, MO

Thanks again! Wink

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