ADS7871 I/O ports Output troubles

Any ideas on this one guys?  Each chip does the same thing.

Hi Michael,

Sorry for the delay. A few questions:

- Just to be clear, do you read the correct value from reg address 6 after you've written to it?
- What do you have connected to the ADC IO pins on your board? Could you post a schematic showing the ADC block?
- Are you using any special operating modes; 16 bit R/W, CS always low, etc.?
- Could you also share the part of your code where you configure the ADC registers and exercise the GPIOs?

Any other data or scope plots that you've gathered and would like to share would be helpful.

Best Regards,
Harsha Munikoti

Welp I'm just as late responding as you.  I've blue wired a GPIO from my MSP430 to get around the problem, but few blue wires the better...

Do I read the correct value from reg 6?  Yes.  I write 0x00 to it expecting all ports to be output.

What is connected to ADC IO?  A counter.  It resets the counter when the conversion is complete.

CS is always low (GND).  I'm using biniary mode 14-bit ADC.

Code to initADC()

void initADC(void) {

unsigned char read=0;

//write Serial Control register
write8ADC (0x18, 0x00);

//write ADC Control Register
write8ADC (0x03, 0x20);

//write gain/MUX register
write8ADC(0x04, 0x0D);

//write DIO CTRL register
write8ADC(0x06, 0x00);
read = read8ADC(0x06);
while (read!=0x00);

//write REF/OSC register
write8ADC(0x07, 0x0C);

//write DIO register
// write8ADC(0x05, 0x0F);
}

void write8ADC (unsigned char addr, unsigned char write) {
unsigned char value;
do {
syncADC();

while (!(UCA0IFG&UCTXIFG)); //wait for TX buffer to be ready
UCA0TXBUF = addr; //address
while (!(UCA0IFG&UCTXIFG)); //wait for TX buffer to be ready
UCA0TXBUF = write; //binary output

//confirm write happened
value = read8ADC(addr);
} while (value != write); //trap if value didn't write

}

void syncADC(void) {
unsigned char i;

//sync ADC
for(i=0; i<6; i++) {
while (!(UCA0IFG&UCTXIFG)); // USCI_A0 TX buffer ready?
UCA0TXBUF = 0x00;
}
while (!(UCA0IFG&UCTXIFG)); // USCI_A0 TX buffer ready?
UCA0TXBUF = 0x01;
}

7382.DTRA ADC.pdf

Thank you Harsha,

I thought you'd comment on the value of reg 6 right after I sent it.  You see I blue wired I_O0 to an MSP430 I/0 and therefor wanted to see high impedance from the ADC which is why it was set to input.  I have tried setting reg6 to 0x0F and 0xFF with no success.  I will take a board and connect /CS to an GIO and see what happens, but on page 18 Reset section last paragraph states:

For applications where CS cannot be cycled and system synchronization is lost, the ADS7871 must be reset
by writing 39 zeros and a one. The serial interface is then ready to accept the next command byte. This string
length is based on the worst case conditions to ensure that the device is synchronized.

Hence my syncADC() function.  I read reg6 twice before attempting to write to it, and according to the note on the same page that ringing would be masked by scope probes meaning it should work when I'm probing on the signals to watch its communication.

But let's debug...

1.  Change reg6 to 0xF and try again.

2.  Connect /CS to GIO and try again.

3.  Probe SCLK, MOSI, MISO, and /CS to confirm proper interaction.

4.  Read reg6 many times before writing to reg5.

and...hike!

BTW...I'm using CC4305137 and CCS6.0.0.00190, not that this is a 430 problem.

#2 did it!

Thanks...