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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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 Posted: Wed Apr 21, 2010 11:42 pm |
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Your read routine doesn't look correct. The data sheet shows the read
operation in Figure 2 on page 12:
http://focus.ti.com/lit/ds/symlink/ads1112.pdf
It shows only 3 bytes that may be read from the ADS1112. The last one
of those 3 is optional. So only 2 bytes really need to be read. See my
proposed routine below. It reads the two bytes, combines them into a
16-bit word, and then returns the word. It does not return the A/D result
in global variables. The proper way to return a result from a function
is with a 'return' statement.
Also, this being a Burr-Brown data sheet for i2c, it doesn't show a NACK
on the last i2c read. But, doing a NACK on the last read is the standard
for i2c operations, as described in the i2c spec.
The ADS1112 data sheet says this, regarding the first byte which was read:
| Quote: |
Similarly, when a master has finished reading a byte,
it pulls SDA LOW to acknowledge this to the slave.
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They're referring to doing an ACK on the first i2c_read() operation.
Fair enough.
Then they say this (bottom right on page 8):
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A not-acknowledge is performed by simply leaving SDA
HIGH during an acknowledge cycle.
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However, the context is not clear. Are they referring to the slave
(ADS1112) or the master (the PIC) ?
However, I think you should at least initially, try it with a NACK on the
last i2c read. That's done as indicated below, with a 0x00 parameter
for the i2c_read() function.
| Code: |
int16 ADS1112_Read(void)
{
int8 lsb, msb;
int16 retval;
i2c_start();
i2c_write(ADS1112_ID_R);
msb = i2c_read();
lsb = i2c_read(0); // Do a NACK on the last read
i2c_stop();
retval = make16(msb, lsb);
return(retval);
}
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Then you would call the read routine in a loop in main() and display
the ADC value that was read. In the code below, 'result' must be
declared as an 'int16' at the start of main(). And of course you
need to call your config routine before entering this loop.
| Code: |
while(1)
{
result = ADS1112_Read();
printf("%lu \n\r", result);
delay_ms(500);
} |
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MAC
Joined: 21 Apr 2010
Posts: 3
Location: Stevenage Herts UK
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| I2C PIC to Device Beginner Issues |
| Posted: Thu Apr 22, 2010 2:31 am |
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Thank you for the response,
I will try out the this method and get back tonight.
MAC
_________________
Every day above ground is a great day! |
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MAC
Joined: 21 Apr 2010
Posts: 3
Location: Stevenage Herts UK
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| i2c pic16f876 to ads1112 |
| Posted: Thu Apr 22, 2010 12:32 pm |
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Hi PCM programmer
Thank you for your pointers, it certainly helps.
The device is continuously sending FFFF so maybe the device has blown. Need to get a new device.
Cheers |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Thu Apr 22, 2010 12:51 pm |
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Run this program and see if finds the ADS1112 chip. This program will
report any i2c chips that are on the bus, if they're alive (within the slave
address range of 0x10 to 0xEF). If it doesn't find it make sure that pins
A0 and A1 are connected to ground on the ADS1112.
Also, make sure you have pull-up resistors on the SDA and SCL lines.
You can use 4.7K ohm resistors.
| Code: |
#include <16F877.h>
#fuses XT,NOWDT,NOPROTECT,PUT,NOLVP,NOBROWNOUT
#use delay(clock=4000000)
#use i2c(Master, sda=PIN_C4, scl=PIN_C3)
#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7, ERRORS)
// This function writes the slave address to the i2c bus.
// If a slave chip is at that address, it should respond to
// this with an "ACK". This function returns TRUE if an
// ACK was found. Otherwise it returns FALSE.
int8 get_ack_status(int8 address)
{
int8 status;
i2c_start();
status = i2c_write(address); // Status = 0 if got an ACK
i2c_stop();
if(status == 0)
return(TRUE);
else
return(FALSE);
}
//=================================
void main()
{
int8 i;
int8 status;
int8 count = 0;
printf("Start:\n\r");
delay_ms(1000);
// Try all slave addresses from 0x10 to 0xEF.
// See if we get a response from any slaves
// that may be on the i2c bus.
for(i=0x10; i < 0xF0; i+=2)
{
status = get_ack_status(i);
if(status == TRUE)
{
printf("ACK addr: %X", i);
count++;
delay_ms(2000);
}
}
if(count == 0)
printf("\n\rNothing Found");
else
printf("\n\rFound %u chips", count);
while(1);
} |
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