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Foppie
Joined: 16 Sep 2005
Posts: 138
Location: The Netherlands
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| DA conversion |
 Posted: Fri Sep 16, 2005 6:27 am |
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Hello,
I coded a PIC16F877A so that it could make a Analog Output Signal using an AD5312 chip but it doesn't seem to work. Has anybody have any suggestions?
my code:
| Code: | #device PIC16F877A *=16 ADC=8
#include <drivers/16f877.h>
#FUSES NOWDT //No Watch Dog Timer
#FUSES HS //High speed Osc (> 4mhz)
#FUSES NOPROTECT //Code not protected from reading
#FUSES NOLVP //Low Voltage Programming on B3
#FUSES NOCPD //No EE protection
#FUSES NOWRT //Program memory not write protected
#use delay(clock=20000000)
#use rs232(baud=9600, BRGH1OK, parity=n, bits=8, xmit=PIN_C6, rcv=PIN_C7)
//LED
#define LED PIN_D7 // LED Output (D1)
#define LED1 PIN_D0 // LED 1 Output (D6)
#define LED2 PIN_D1 // LED 2 Output (D5)
#define LED3 PIN_D2 // LED 3 Output (D7)
#define LED4 PIN_D3 // LED 4 Output (D8)
//DAC (U10, U9)
#define DAC_LDAC PIN_B4 // Load DAC signal
#define CS_DAC PIN_B2 // Chip select signal for DAC
#define SDI PIN_C4 // SPI Data In
#define CLK PIN_C3 // SPI Clock
void SPI_clockcycle()
// Version 1.0 12.9.2005
// Input : void
// Output : void
// Action : takes clocksignal low and high
{
output_low(CLK);
delay_us(20);
output_high(CLK);
delay_us(20);
}
void SPI_writebit(short data)
// Version 1.0 12.9.2005
// Input : void
// Output : void
// Action : puts a bit on the data in bus
{
if(data)
output_high(SDI);
else
output_low(SDI);
delay_us(10);
SPI_clockcycle();
}
void DAC_convert(short outputSelect, long data)
// Version 1.0 12.9.2005
// Version 1.1 13.9.2005
// - revised parameters (from 1,1,1,1,8,1,1 to 1,16)
// Input : outputSelect- select output A (0) or output B (1)
// data - Data bytes (6 MSb get negated)
// Output : void
// Action : converts a digital (10 bits) value to a analog output
{
long i;
delay_us(20);
output_high(CLK); //SCLK pulse signal
delay_us(20);
output_low(CS_DAC); //SYNC input signal
delay_us(20);
//write control bits
SPI_writebit(outputSelect);
SPI_writebit(1);
SPI_writebit(0);
SPI_writebit(0);
output_low(DAC_LDAC);
//write 10 databits
for(i = 0b1000000000; i; i >>= 1)
{
SPI_writebit(i == (data & i));
}
//write last 2 bits to complete total of 16 (sending zeros)
output_low(SDI);
SPI_clockcycle();
SPI_clockcycle();
output_high(CS_DAC);
//put value on line out
delay_us(20);
output_high(DAC_LDAC);
}
void init()
// Version 1.0 12.9.2005
// Input : void
// Output : void
// Action : initializes program
{
ADC_init(); // initializes ADC
output_high(CS_DAC); // makes sure DAC is not selected
output_high(DAC_LDAC);
output_high(CS_USART); // makes sure USART is not selected
output_low(IRQ_USART);
}
void testDAC()
{
short ledon = TRUE;
int i = 0;
while(1)
{
ledon = !ledon;
DAC_convert(0,i * 4000);
DAC_convert(1,i * 4000);
i++;
if (i > 15)
{
i = 0;
}
delay_ms(500);
ChangeLed(LED1, ledon);
ChangeLed(LED2, ledon);
ChangeLed(LED3, ledon);
ChangeLed(LED4, ledon);
}
}
void main()
{
ChangeLed(LED, TRUE);
init();
testDAC();
} |
when I run the code the Main Led is continually on and the other 4 leds are blinking as expected but there doesn't seem to be any other activity. I can not even find any other changing signals on the board.
Please help |
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rwyoung
Joined: 12 Nov 2003
Posts: 563
Location: Lawrence, KS USA
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| Posted: Fri Sep 16, 2005 7:12 am |
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In your main() you need to prevent the PIC from hitting the SLEEP instruction compiled after your last function call. Add
as your last statement and try again.
_________________
Rob Young
The Screw-Up Fairy may just visit you but he has crashed on my couch for the last month! |
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Ttelmah
Guest
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| Posted: Fri Sep 16, 2005 7:34 am |
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That shouldn't apply. His 'TestDAC' function contains an endless loop, so never returns.
However the code is not posted for 'ChangeLed', making working out what is going on hard.
One obvious question is how the activity is being 'looked' for, since with the long (500mSec) delay in this loop, the activity on the DAC lines, is going to be very hard to see, without a digital, or storage sope.
Best Wishes |
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rwyoung
Joined: 12 Nov 2003
Posts: 563
Location: Lawrence, KS USA
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| Posted: Fri Sep 16, 2005 1:31 pm |
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| Ttelmah wrote: | | That shouldn't apply. His 'TestDAC' function contains an endless loop, so never returns. |
Yep, shouldn't scroll through the listing so fast next time.
For 16F877 parts I generally enable the power up timer (PUT fuse).
If you look at the SPI lines, do you see a clock (use an oscilloscope, not a DMM)?
Are you sure you are intpreting the datasheet for the DAC correctly? You have a pin named "SDI" but generally that would be the INPUT data pin to the PIC's SPI port and the PIC would then have a pin called SDO which is its output bit. The PIC (master) connects its SDO to the DAC's (slave) SDI pin. Personally I prefer the Motorola terms MOSI (Master Out, Slave IN) and MISO (Master In, Slave Out) for labeling SPI pin eventhough they aren't what "true" SPI parts call the signals. MOSI/MISO are very descripting and you KNOW exactly where the signals are supposed to go.
_________________
Rob Young
The Screw-Up Fairy may just visit you but he has crashed on my couch for the last month! |
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Guest
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| Posted: Mon Sep 19, 2005 12:30 am |
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| Ttelmah wrote: | | However the code is not posted for 'ChangeLed', making working out what is going on hard. |
Sorry, forgot to post that code.
| Code: | void ChangeLed(int channel, short led_on)
// Version 1.0 8.9.2005
// Input : channel - address of led
// led_on - state of led
// Output : void
// Action : Set or clear specified Leds.
// Using in main program like ex. ChangeLed(LED1,FALSE); then led 1 is off
{
if (led_on)
{switch (channel)
{
case LED: output_high(LED);
break;
case LED1: output_high(LED1);
break;
case LED2: output_high(LED2);
break;
case LED3: output_high(LED3);
break;
case LED4: output_high(LED4);
break;
}
}
else
{
switch (channel)
{
case LED: output_low(LED);
break;
case LED1: output_low(LED1);
break;
case LED2: output_low(LED2);
break;
case LED3: output_low(LED3);
break;
case LED4: output_low(LED4);
break;
}
}
} |
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Foppie
Joined: 16 Sep 2005
Posts: 138
Location: The Netherlands
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| Posted: Mon Sep 19, 2005 4:06 am |
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| Ttelmah wrote: | | One obvious question is how the activity is being 'looked' for, since with the long (500mSec) delay in this loop, the activity on the DAC lines, is going to be very hard to see, without a digital, or storage scope. |
I will do that, but I'll have to get one... But I was assuming I could just look at the output from my circuit, that should get higher (in steps) and after approximatly 7.5 seconds dropping low again.
I now have only a DMM but tomorrow I'll try to get my hands on a scope |
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Foppie
Joined: 16 Sep 2005
Posts: 138
Location: The Netherlands
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| Posted: Mon Sep 19, 2005 4:22 am |
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| rwyoung wrote: | | Are you sure you are intpreting the datasheet for the DAC correctly? You have a pin named "SDI" but generally that would be the INPUT data pin to the PIC's SPI port and the PIC would then have a pin called SDO which is its output bit. The PIC (master) connects its SDO to the DAC's (slave) SDI pin. Personally I prefer the Motorola terms MOSI (Master Out, Slave IN) and MISO (Master In, Slave Out) for labeling SPI pin eventhough they aren't what "true" SPI parts call the signals. MOSI/MISO are very descripting and you KNOW exactly where the signals are supposed to go. |
I changed SDI for SDO and now it seems to react! (I changed it earlier today but didn't realize my code was stuck on another place so I didn't see the result directly...) I'm still gonna check it with a scope as soon as I have one. I'll post if I know it is (not) working.
But so far, so good!
Ttelmah and rwyoung thanks for your help so far! |
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Foppie
Joined: 16 Sep 2005
Posts: 138
Location: The Netherlands
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| Posted: Tue Sep 20, 2005 2:06 am |
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It is working 
Thanks again for all your help!
I'll never forget MOSI/MISO and a good scope! |
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