PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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 Posted: Tue Apr 20, 2010 3:46 pm |
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The 12F675 doesn't have a CCP module, so if you want to measure
the pulse width, you need to do it in software. The following program
takes the ASM code from the PicBasic Pro PULSIN command and puts it
in a function "wrapper" so it can be used with CCS. This code can be
used to measure the pulse width of a signal on any PIC input pin.
The program below will work with your 50 Hz signal. Pulse widths
will vary from 0 to about 20 ms. The accuracy is within 4%.
This is the test program. It should be saved as "pulsin_test.c".
| Code: |
#include <16F877.H>
#fuses XT, NOWDT, BROWNOUT, PUT, NOLVP
#use delay(clock=4000000)
#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7, ERRORS)
#include "pulsin.c"
//======================================
void main()
{
int16 result;
int16 pulse_width_usec;
// Measure the pulse width of the signal on pin B0.
// The pulse width is displayed in microseconds.
while(1)
{
result = pulsin(PIN_B0, 1);
pulse_width_usec = result * 10;
printf("%lu\n\r", pulse_width_usec);
delay_ms(500);
}
}
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This is the Pulsin driver code. It should be saved as "pulsin.c".
| Code: |
#ifdef __PCB__
#error Pulsin is not supported for the PCB compiler.
#endif
#ifdef __PCD__
#error Pulsin is not supported for the PCD compiler.
#endif
#ifdef __PCM__
#define interrupt_enabled(x) !!(*make8(x,1) & make8(x,0))
#endif
#ifdef __PCH__
#define interrupt_enabled(x) !!(*(make8(x,1) | 0xF00) & make8(x,0))
#endif
#define BYTE_PTR(x) &(int8 *)(x)
// ASM definitions
#define W 0
#define F 1
// Status Register Bits
#define Z 2
#define C 0
#ifdef __PCM__
// Register addresses (16F)
#byte INDF = 0x00
#byte STATUS = 0x03
#byte FSR = 0x04
#endif
#ifdef __PCH__
// Register addresses (18F)
#byte INDF0 = 0xFEF
#byte STATUS = 0xFD8
#byte FSR0H = 0xFEA
#byte FSR0L = 0xFE9
#endif
//---------------------------------------
// #define PULSIN_MAX 60000
#ifdef PULSIN_MAX
#if(PULSIN_MAX > 65535)
#error PULSIN MAX is too High. Maximum value is 65535.
#endif
#endif
//---------------------------------------
#ifdef __PCM__
int16 pulsin(int8 ccs_pin, int8 state)
{
int8 io_port;
#endif
#ifdef __PCH__
int16 pulsin(int16 ccs_pin, int8 state)
{
int16 io_port;
#endif
int8 const bitmask_table[] = {0x01,0x02,0x04,0x08,0x10,0x20,0x40,0x80};
int8 gie_enabled = FALSE;
int8 bitmask;
int8 flip;
int16 count;
// These variables are used in the ASM code
// and must be located in the same RAM bank.
#locate io_port = 0x30 // Can be 8 or 16 bits
#locate count = 0x32 // 16 bits
#locate state = 0x34
#locate bitmask = 0x35
#locate flip = 0x36
if(interrupt_enabled(GLOBAL))
{
disable_interrupts(GLOBAL);
gie_enabled = TRUE;
}
// Get the I/O Port address and the bitmask from
// the CCS pin number value.
io_port = ccs_pin >> 3;
bitmask = bitmask_table[ccs_pin & 7];
// Set TRIS = input.
#ifdef __PCM__
*(io_port | 0x80) |= bitmask; // For 16F PICs
#endif
#ifdef __PCH__
*(io_port + 0x12) |= bitmask; // For 18F PICs
#endif
#asm
PULSINT:
#ifdef __PCM__
movf io_port, W ; Get port
movwf FSR
#endif
#ifdef __PCH__
movf io_port, W ; Get port lsb
movwf FSR0L
movf BYTE_PTR(io_port) +1, W ; Get port msb
movwf FSR0H
#endif
movf bitmask,w
clrf flip ; Preset state tracking
btfss state, 0 ; State tracking preset for flip
movwf flip ; Set state to bit mask
call statecnt ; Wait for idle state
btfsc STATUS, Z ; If timeout then it's over
goto done
call statecnt ; Wait for starting edge
btfsc STATUS, Z ; If timeout then it's over
goto done
call statecnt ; Do the count
goto done
//--------------------------------------------------
statecnt:
movf bitmask, W ; Flip state each time through here
xorwf flip, F
#ifdef PULSIN_MAX
movlw ((-(PULSIN_MAX)) + 1) ; Start counter -PULSIN_MAX + 1
movwf count
movlw (((-(PULSIN_MAX)) + 1) >> 8)
movwf BYTE_PTR(count) + 1
#else
movlw 1
movwf count
clrf BYTE_PTR(count) + 1
#endif
statecntloop: ; Takes 10 usec
#ifdef __PCM__
movf INDF, W ; 1 Read Port with INDF
#endif
#ifdef __PCH__
movf INDF0, W ; 1 Read Port with INDF0
#endif
andwf bitmask, W ; 1 Mask it with bitmask
xorwf flip, W ; 1 Mix with desired state
btfss STATUS, Z ; 2 / 1
#ifdef PULSIN_MAX
goto statecntexit ; 0 / 2 No longer in state
#else
return ; 0 / 2 No longer in state
#endif
incf count, F ; 1 Increment counter
btfsc STATUS, Z ; 1 / 2
incfsz BYTE_PTR(count) + 1, F ; 1 / 2
goto statecntloop ; 2 / 0
return ; 0 / 2 Counter overflow
#ifdef PULSIN_MAX
statecntexit:
movlw PULSIN_MAX ; Normalize count
addwf count, F
movlw PULSIN_MAX >> 8
btfsc STATUS, C
addlw 1
addwf BYTE_PTR(count) + 1, F
bcf STATUS, Z ; Indicate no overflow
return
#endif
done:
#endasm
if(gie_enabled)
{
enable_interrupts(GLOBAL);
}
return(count);
}
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For reference, here is the PicBasic COUNT command for CCS:
http://www.ccsinfo.com/forum/viewtopic.php?t=41877 |
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