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cchappyboy
Joined: 03 Dec 2008
Posts: 45
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| Question about use pin as uart rcv port and normal input. |
 Posted: Wed Apr 14, 2010 9:26 am |
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I used pic16f84a.
I want to use pin_b2 as uart receiving port, and normal output pin during a loop. I set
| Code: | #use rs232 (baud=9600,xmit=pin_b1,rcv=pin_b2)
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at the beginning of the program. Do I need to do something before I let
pin_b2 be as normal input pin in that loop ? And after that do I need use
| Code: | #use rs232 (baud=9600,xmit=pin_b1,rcv=pin_b2)
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to let this pin be as a uart receiving port again ?
I appreciate any response in advance. |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Wed Apr 14, 2010 11:56 am |
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I'm not sure why you want to do this, because if you have the PIC
and a MAX232 both driving the same line, then you can have a
conflict. It's possible that some damage could occur to the chips.
But anyway, here is how you can find the answer:
Make a small test program that only tests your desired feature.
In the Project Options, put the .LST file format into Symbolic format.
This will make it easier to read. Then compile the program and look
at the .LST file:
In this part, we see that the compiler sets the TRIS for pin B2 to be
an output pin. That is normal.
| Code: |
.................... c = getc();
0030: CALL @GETCH_1_
0031: MOVF @0D,W
0032: MOVWF c
.................... output_low(PIN_B2);
0033: BSF STATUS.RP0
0034: BCF TRISB.2 // Set TRISB.2 = 0 (set as output pin)
0035: BCF STATUS.RP0
0036: BCF PORTB.2
.................... c = getc();
0037: CALL @GETCH_1_
0038: MOVF @0D,W
0039: MOVWF c
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In the RS232 library code, CCS sets pin B2 to be an input pin, before
it executes the RS232 code for getc(). So it will work OK for RS232.
So the answer is, no, you don't need to use another #use rs232()
statement each time. Just use one statement.
| Code: |
.................... #use rs232 (baud=9600,xmit=pin_b1,rcv=pin_b2)
0004: BSF STATUS.RP0
0005: BSF TRISB.2 // Set TRISB.2 = 1 (set as input pin)
0006: BCF STATUS.RP0
0007: BTFSC PORTB.2
0008: GOTO 007
0009: MOVLW 08
000A: MOVWF @0C
000B: CLRF @@12
000C: BSF @0C.7
000D: GOTO 01C
.
.
.
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Here is the test program:
| Code: |
#include <16F84a.H>
#fuses XT, NOWDT
#use delay(clock=4000000)
#use rs232 (baud=9600,xmit=pin_b1,rcv=pin_b2)
//========================================
void main()
{
char c;
c = getc();
output_low(PIN_B2);
c = getc();
while(1);
}
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cchappyboy
Joined: 03 Dec 2008
Posts: 45
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| Posted: Thu Apr 15, 2010 12:04 pm |
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| Thank you so much. By the way, where can i get the library code such as rs232 or something else supplied by ccs. |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Thu Apr 15, 2010 12:12 pm |
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The C source code is not available for the #use rs232() library.
CCS does not supply it.
If you want to understand the library code, you can look in the .LST file.
It shows the ASM code for the #use rs232() library.
Also, here is some C source code that duplicates the function of the
#use rs232() library.
http://www.ccsinfo.com/forum/viewtopic.php?t=26631&start=8
However, it's preferable that you use the library code. The code above
was only intended to help someone who had a buggy version of the
compiler. |
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