PIN input read at a certain frequency

ela_vasiliu · Joined: 18 Jun 2010 Posts: 3

Hy,

It is the first that I'm working with PICC Compiler and I need some help.

I want to read the input signal on C7 PIN of PIC18F452 at a certain frequency using rs232. Can anyone help me with some example code.

Thanks.

Ela
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Ela

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

Are you trying to read a serial byte with the usual Start & Stop bits, or do you want to read an arbitrary string of bits?
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Wayne_ · Joined: 10 Oct 2007 Posts: 681

Not sure what you want to do:-

Do you want to read pin C7 every second via RS232 or do you want to read the frequency of the signal on pin C7 via RS232 ?

pmuldoon · Joined: 26 Sep 2003 Posts: 218 Location: Northern Indiana

The design specs seem a little vague.

ela_vasiliu · Joined: 18 Jun 2010 Posts: 3

So, I want to read the signal on C7 Pin via rs232. My signal has the frequency of 1200Hz and i want to make 16 or 32 readings in each period of the signal.

Sorry if I'm not that explicit but as I've said before I'm a beginner.

Thanks
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Ela

pmuldoon · Joined: 26 Sep 2003 Posts: 218 Location: Northern Indiana

You will need to find out the RS232 properties (baud-parity-stop bits) of the device that is sending the data so you can set up the PIC properly.

You also must match the devices electrical specs. Usually to communicate with an RS232 device you will need something like a MAX232 chip to match signal voltage levels, unless the other device is putting out a TTL level signal.

Then you need to interpret the data coming in. Is it one byte? two bytes? 100 bytes?

Start by looking up the #USE RS232 directive in your manual. Then you can ask more specific questions.

ela_vasiliu · Joined: 18 Jun 2010 Posts: 3

My signal is serial bus of bits, they come in groups of 9 or 18 bits
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Ela

collink · Joined: 08 Jan 2010 Posts: 137 Location: Michigan

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

pmuldoon · Joined: 26 Sep 2003 Posts: 218 Location: Northern Indiana

It may not even be a valid RS232 signal. It may just be a string of bits.
Maybe it randomly determines whether to send 9 or 18 bits. Maybe they're half-bits with positive or negative spin. See what happens when I'm left to my imagination!

FvM · Joined: 27 Aug 2008 Posts: 2337 Location: Germany

It should work, if you set the USART to synchronous Master Mode with continuous reception. Consult the PIC18F452 datasheet for details.

From the CCS doc, it can be expected that #use rs232 with SYNC_MASTER_CONT option is supporting the intended operation.

pmuldoon · Joined: 26 Sep 2003 Posts: 218 Location: Northern Indiana

collink · Joined: 08 Jan 2010 Posts: 137 Location: Michigan