I'm trying to make sure I have it wired up properly, because I am seeing very odd outputs from my DOUT (MISO) pin and I think it may be connected to my wiring. On a rare occasion I get a good set of pulses, but sometimes I get a pulse or two (more often none) and then it goes high and slowly trickles down.. but not nice and smooth like a capacitor discharging, its rough and jagged.. almost like slanted steps, or sometimes it looks like there are pulses in there, but very small.

Here is my wiring:

SCLK -> SCLK

CS -> SS

MCLKIN -> CMOS CLK @ 12MHz

MCLKOUT -> OPEN

RESET -> 5V

AVdd -> 5V

AINCOMM/P0 -> OPEN (IS THIS CORRECT?)

SYNC/P1 -> OPEN (IS THIS CORRECT?)

AIN0-7 -> OPEN EXCEPT AIN7 CONNECTED TO SIGNAL

MUXOUT(+) -> ADCIN(+)

MUXOUT(-) -> ADCIN(-)

REFIN(+) -> 2.5V (WELL 2.38V, I'm driving it from a 5V source with a resistor divider but its consuming a lot of current so I had to adjust from using 100kohms to 1kohms.. don't know if this could be part of the problem, datasheet states it only consumes 400uA?)

AGND -> GND

RDY -> ISR triggered on an inverted rising edge

DOUT -> MISO

DIN -> MOSI

DVdd -> 5V

DGNG -> GND

are these correct? I used this datasheet to wire it up:

http://www.analog.com/media/en/technical-documentation/data-sheets/AD7738.pdf

I really need this working.. it almost seems as if I have either not connected something properly, or my MCU is messing up.. but I don't think thats the case since its worked fine until now.

Also the RDY signal seems to work when its supposed to.

thanks,

scarlson

Update: added o-scope pictures and tried tying P1 both high and low with same result.

SCLK(teal) DIN(blue) DOUT(pink) SS(yellow) request for data

initial setup

  • 1
    Schematic, oscilloscope screenshots, code, data would make you question clearer. Verbal descriptions aren't particularly useful. – Nick Alexeev Nov 18 '15 at 19:57
  • I will upload a o-scope screenshots tonight, and anything else pertinent. – scarlso9 Nov 18 '15 at 20:00
  • Datasheet p.7, pin P1 "When configured as an input, should be tied high or low". What are you writing to the I/O port register? ... REFIN, if noisy, might affect accuracy but shouldn't affect basic operation. – Brian Drummond Nov 18 '15 at 20:09
  • ..I think that may be part of my confusion. I don't understand what I should be doing with P1 or P0.. I am writing 0x01 to enable writing to the I/O port register and then I am writing 0xF0 to configure the port register. – scarlso9 Nov 18 '15 at 21:23
  • Could it be my chip is fried? I don't have another to test, but I would surprised if I did anything to damage it unless my pin configuration above is wrong.. – scarlso9 Nov 19 '15 at 1:01

For anyone that has a similar question, I was not sending 0x00 so my ss line was never going low so the MISO (DOUT) was never given a chance to send anything. one thing that does bother me however, is the discharge that DOUT experiences, although I am still getting the correct values it seems this is just how it works.

Also specific to this chip I grounded AINCOMM/P0 and SYNC/P1, which seems to work, AINCOMM is the analog reference voltage when the ADC is configured in single ended mode. SYNC/P1 is just tied High or Low, in my case I decided (arbitrarily) to tie it to 0.

Hope this helps someone out!

-scarlson

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