Serial Communication RS232

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Hasnatsaeed

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Hi.i am trying to communicate with 16f877a via serial port .The problem is that nothing is happening.the code is simple and its working 100% fine(compiling and simulating).i am using the CCS compiler so that everything is in C.i have attached the source file and the design.kindly debug it.i am desperate about it.thank u
 

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Just checking you circuit diagram.. Pin 5 on the com connector isn't connected to ground. Is this just a drawing mistake as this does need to be grounded in the real world.

Ian
 
Hi, you want to check out the output in the virtual terminal? Right? Or are you using a virtual com port for viewing it in an application?

First if all, MCLRE is floating, no code will be executed. Pull it high.

What is the oscillator frequency that you have set for the processor? Also check out the baudrate set in the virtual terminal properties.
 
The processor frequency is 20MHz......and my baud rate is 9600...the same is in the hyper terminal i setup...i just want to see the output on hyper terminal simple.nothing more or less but nothing appears.some say that may be my processor's frequency is not compatible with the baud rate i am using or it may be the capacitor's compatiblity with the baud rate..i could not understand either of these.plz help
 

Did you connect #5 of the connector to 0V as explained by Ian.??

EDIT.
The pin outs
 

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How did you simulate this.. in ISIS ( I've seen ISIS in the picture posted ) it looks like you had the virtual terminal connected. Was it ok like this?
 
Hasnatsaeed said:
yes i did connect to the ground
Click to expand...

hi,
OK.
Even with different baud rates set for the two devices, most often you should see corrupted characters on the PC terminal.

With the 20MHz xtal and for a 9600 baud rate, what are BRGH and SPBRG set to in the PIC.?
 
i dont know...i never set it...i built a project in CCS and it never asked for such things..all it asked was baudrate,parity etc.i am attaching a picture of the configurations i set before compiling the project
 

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some of my friends implemented the serial communication using atmel and they were having the same problem but when they changed their capacitors ,that were attached to max 232 ,from 10 uf to 11 uf..it worked...so i was wondering if mine is the same problem?
 

I have used capacitor values from 1uF thru 10uF and never had a problem

Do you have access to an oscilloscope.?
 
Last edited:
was it with pic16f877a?......i too used 10 uf capacitors b4 shifting to 22uf but no difference.still nothing...yes i do have an access to an oscilloscope
 
Hasnatsaeed said:
was it with pic16f877a?......i too used 10 uf capacitors b4 shifting to 22uf but no difference.still nothing...yes i do have an access to an oscilloscope
Click to expand...

Use the scope to monitor the pins into and out of the MAX232.

On the PIC side of the MAX the signals should swing from +5V to 0V and on the PC side approx +/9V swing, when a data string is being sent and received.

The display pattern on the scope should change as the data changes..

Do you follow OK.?
 
yes i do..you i should connected the oscilloscope's positive probe on TX pin of the pic16f877a?.chk it..and then connect the probe to the output pin of max232?.and chk it..is that what you are saying?
 
Hasnatsaeed said:
yes i do..you i should connected the oscilloscope's positive probe on TX pin of the pic16f877a?.chk it..and then connect the probe to the output pin of max232?.and chk it..is that what you are saying?
Click to expand...

Connect the 0V side of the scope probe to the 0V of the PIC and MAX, use the tip of the scope probe to measure the different pins, signals
 
On a side note... what's the RS232 chips part no..This rings a bell... The RS232 chip I'm using now uses 0.1uf caps, not 10uf.. Have you checked the datasheet...
 
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