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RS232 receive

 
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tmach



Joined: 20 Dec 2003
Posts: 14

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RS232 receive
PostPosted: Sun Mar 07, 2004 2:44 pm     Reply with quote
Hello,
I want to setup RS232 communication between two 16F874A pic's. Both the pics are running from a 20MHz osc in HS mode. The Tx port of the Master is connected to the Rx port of the slave.
The master sends the serial data @15200bps using the following command:
printf("%2X%2X%2X%2X%2X%2X%2X%2X%2X%2X%2X%2X%2X%2X%2X%2X%2X%2X", Tx1_L,Tx1_H,Rx1_L,Rx1_H,Tx2_L,Tx2_H,Rx2_L,
Rx2_H,CH0_L,CH0_H, CH1_L,CH1_H,CH2_L,CH2_H,CH4_L,CH4_H,CH5_L,
CH5_H,CH6_L,CH6_H);
I need to collect this data. I can also select the slave before the master starts the transmission using a strobe signal connected to external interrupt pin of the slave. Please advice if this is possible.

Thanks.
mach
Ttelmah
Guest
Re: RS232 receive
PostPosted: Sun Mar 07, 2004 3:48 pm     Reply with quote
tmach wrote:
Hello,
I want to setup RS232 communication between two 16F874A pic's. Both the pics are running from a 20MHz osc in HS mode. The Tx port of the Master is connected to the Rx port of the slave.
The master sends the serial data @15200bps using the following command:
printf("%2X%2X%2X%2X%2X%2X%2X%2X%2X%2X%2X%2X%2X%2X%2X%2X%2X%2X", Tx1_L,Tx1_H,Rx1_L,Rx1_H,Tx2_L,Tx2_H,Rx2_L,
Rx2_H,CH0_L,CH0_H, CH1_L,CH1_H,CH2_L,CH2_H,CH4_L,CH4_H,CH5_L,
CH5_H,CH6_L,CH6_H);
I need to collect this data. I can also select the slave before the master starts the transmission using a strobe signal connected to external interrupt pin of the slave. Please advice if this is possible.

Thanks.
mach

Switch to using %02X for each variable. This way two characters are sent for each variable, where the 'as shown' version, will 'lose' digits if there is a leading zero.
Then _given your synchronisation allready mentioned_ (otherwise consider adding a 'header' so the data is recognised), you can just pull 'pairs' of digits into successive variables. So something like:

Code:

#define fromhex(x) ((x>'9')?((x & 0xF)+10):(x-'0')

int8 gettwodigits() {
    int8 val1;
    int8 val2;
    val1=getc();
    val2=getc();
    return(fromhex(val2)+fromhex(val1)*16);
}


Call this as many times as necessary to pull all the variables.

Personally, I'd consider using buffered serial I/O, and adding a 'timeout', so that the system will recover cleanly, if the data is corrupted.

Best Wishes
Ernest LKL
Guest
Using PIC to acquire serial data from PC
PostPosted: Tue Mar 30, 2004 2:58 am     Reply with quote
Hello,

I am having some problem trying to acquire a stream of serial data from a software in PC. Looking at the results using Hyperterminal, the software will output the readings of the sensors (termistor & humidity sensor) every 100 ms.
eg.:

"Temperature: 23.7 C Humidity: 61.3 %"

So, how can I actually acquire the values of the temperature and humidy using PIC 16F877A? How do we segregate the values and the text?

How do we implement the buffering for the serial data and adding a timeout?

Thanks a lot in advance.
Ernest
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