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Guest
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| infrared and 16F77 |
 Posted: Fri Sep 16, 2005 4:36 am |
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hi,
i have problem in sending data via infrared. I use 16F77 PIC, pin A0 to detect switch press, pin C6 to send data to IR LED.
In between I use 12F675 to generate ~38khz freq with 27% duty cycle, and 74HC132 NAND Schmitt. For NAND ic, pin #1 for serial data, pin #2 38khz fed from 12F675, and out-pin # 3 to control 2N4403 PNP transistor, on/off.
Code for 38khz freq:
| Code: |
#include <12F675.h>
#fuses xt, nomclr, noprotect, nowdt, nobrownout
#use delay(clock=4000000) // 4mhz clock
#define HH (output_high(PIN_A2))
#define LL (output_low(PIN_A2))
// 7us(high) + 16us(low) + 3.2us(overhead) = 26.2us
// so, freq = 1/26.2us = 38.16khz ~ 38khz
// *** 3.2us got this info from one of the probs posted, i guess...
#define t_high 7
#define t_low 16
void main() {
while(1) {
// clock = 4,000,000
// system timing = 1/4meg/4 = 1us
HH;
delay_cycles(t_high); // 7us high
LL;
delay_cycles(t_low); // 16us low
}
}
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Code for txmitter:
| Code: |
#include <16F77.h>
#fuses hs, noput, noprotect, nobrownout, nowdt
#use delay(clock=9830400)
#define SEND (!input(PIN_A0)) // switch pressed!
#use rs232 (baud=1200, xmit=PIN_C6, rcv=PIN_C7)
void main() {
const char c='a';
while(1) {
if(SEND) {
putc(c);
delay_ms(250); // debounce
}
}
}
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when I power up the circuit, output from C6 (to NAND pin #1) always 'high' (is this their default state?) ...[1 nand 1 = 0], it will NAND'ed with the input from 38khz freq (NAND pin #2).
so, when I monitor the output (NAND pin #3) using Os-cope, it always turn on/off the 4403.
any help? thanks. |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Fri Sep 16, 2005 11:56 am |
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The idle state for the transmit pin on the Hardware USART is a high level.
To see this, go to the 16F77 data sheet, look in section 10.0 on the USART
and go to Figure 10-2. It shows Pin C6 in a high level idle state, and
when it does a start bit, it goes to a low level.
If you want to make an inverted output UART, then you'll have to
insert an inverter IC in there, or you could configure pins C6 and C7
as a software UART and then use the INVERT parameter. Maybe
you should do that initially, as a proof of concept. Example:
| Code: | | #use rs232(baud=1200, xmit=PIN_C6, rcv=PIN_C7, FORCE_SW, INVERT) |
Of course, you must have a version of the compiler that supports
the FORCE_SW parameter. If you have an earlier version, you
can do it by breaking the #use rs232 statement up into two separate
statements, one for xmit and one for rcv. Then it will become a
soft UART. |
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Guest
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| Posted: Sun Sep 18, 2005 7:24 pm |
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thank you PCM Programmer! it works. by the way, is it possible if I want to implement this code
| Code: |
#use rs232(baud=1200, xmit=PIN_C6, rcv=PIN_C7, FORCE_SW, INVERT)
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to other PICs as well? e.g 16F84A
| Quote: |
If you have an earlier version, you
can do it by breaking the #use rs232 statement up into two separate
statements, one for xmit and one for rcv. Then it will become a
soft UART.
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can u show me an example or is this what u mean
| Code: |
#use rs232(baud=1200, xmit=PIN_C6, FORCE_SW, INVERT)
#use rs232(baud=1200, rcv=PIN_C7)
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Sun Sep 18, 2005 8:57 pm |
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The 16F84a has no hardware UART. CCS always makes a software
UART on any pins you specify. You don't need the FORCE_SW parameter.
There is no need to break up the #use rs232 statement into two
statements.
-----------
If you have more questions beyond this, then post the version of your
compiler. This will be a number such as 2.734, 3.191, or 3.234 etc. |
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