connect AD converter 7903 with SPI from STM32F4

[der-kyle]

Posted on November 02, 2014 at 22:55

Hello,

I want to connect an AD converter AD7903 with the STM32F429 http://www.analog.com/static/imported-files/data_sheets/AD7903.pdf The AD7903 can be driven in a simultaneous sampling mode. It is show in the datasheet on page 25. 1. Im not sure, if I have connect the AD7903 in the right way. I want to connect it, like in the picture. Is that ok, or must I split the clk conduct in CLK from SPI1 and CLK from SPI2? But then I have the problem, that is not be simultaneous. 2. I dont use the MOSI pins. Can I use them as a normaly pin, if I not activate the alternative function of this pin. 3. The maximum datarate of the AD7903 is 1MSPS. Is the STM32F429 with SPI fast enough? I have estimate if f_PCLK = 84MHz and I use a divider of 2, than I get a clock frequency of 42MHz. If I transmit 16Bit I get 42MHz/16 = 2,625 MSPS. Is that ok? 4. Is it possible to get samples of the STM32F429ZIT6 ? I have try it, but I get the answer, that I can buy it by xyv distributor. Thank you very much, for your help in advance Best regards Dirk #ad7903-spi-stm32f429

[Tesla DeLorean]

Posted on November 03, 2014 at 15:13

If you want them to work synchronously, then perhaps you can daisy-chain them and shift the data out as two 16-bit words?

Unless you are a business user of the parts, and have direct sales/support contacts, then yes it's probably cheaper and more efficient to buy your parts directly from the likes of DigiKey or Mouser, or RS/Farnell, or whomever that is in your locality.

[waclawek.jan]

Posted on November 03, 2014 at 15:39

Use one SPI as master and the other as slave, feeding the clock from the master to slave.

> I dont use the MOSI pins. Can I use them as a normaly pin, if I not activate the alternative function of this pin. Yes. > The maximum datarate of the AD7903 is 1MSPS. Is the STM32F429 with SPI fast enough? > I have estimate if f_PCLK = 84MHz and I use a divider of 2, than I get a clock frequency of > 42MHz. If I transmit 16Bit I get 42MHz/16 = 2,625 MSPS. Is that ok? I did not read the datasheet of AD7903, but if the sample/conversion time overlaps the shift out, then yes. However, count on the inflexibility of the SPI clock scheme - you have no other choice than fPCLK/2^N (N=1..8). Also, not all SPI are on the faster APB2 bus. Also, you will need to process the read data, and you have only some 160 cycles per the couple of samples  - whether that is sufficient depends on your particular application. JW

[der-kyle]

Posted on November 03, 2014 at 17:49

Hello,

thank you very much for answering my questions. Best regards Dirk

[der-kyle]

Posted on December 04, 2014 at 19:20

Hello,

I have connected the AD7903 with the STM32F4 in the following way: I want to use a clock speed of 21MHz, because the SPI interface in slave mode has a maximum clock speed of 21MHz. Otherwise I would choose 42MHz. I want to continuously save the data from the AD converter with a clock frequency of 21MHz. I use the DMA2 controller, but I dont know, if this is fast enough to save the data in memory. 1. Can I get problems with the clock speed of 21MHz? 2. Assuming, I would use a clock speed of 42MHz. The same question like under point 1, can I get problems to save the data fast enough? 3. Is it better to split them into DMA controller 1 and DMA controller 2 ? 4. If I use SPI3 and SPI5 both in master mode and ADC1 is to SPI3 and ADC2 is connected to SPI5. Then I have two separate clock wires. Is the clock frequency synchronuos? No, or? Thank you in advance. Best regards, Dirk ________________ Attachments : AD7903_SPI3.png : https://st--c.eu10.content.force.com/sfc/dist/version/download/?oid=00Db0000000YtG6&ids=0680X000006I01b&d=%2Fa%2F0X0000000bSy%2Fcx35IOyNau3NwlR_9YCLM2F2Q5SnvmV8z5on9ChmgNU&asPdf=false

[der-kyle]

Posted on December 04, 2014 at 20:16

[Tesla DeLorean]

Posted on December 05, 2014 at 17:36

You'll have to own your development and experimentation tasks. Your going to have to do these thing to know what is/is not viable for your application.

Yes, suspect 21 MHz would be fine. Short wiring, appropriate grounding and signal paths. DMA, don't see that being an issue the data rate is 1/8 or 1/16 of the bit clocking rate, so bandwidth to memory should be adequate. Transfer enough data so you won't saturate interrupts. ie have a packet length of 100 bytes, use HT/TC DMA interrupts to manage a circular ping/pong operation. Two masters, yes the signals will be synchronous, but probably not in-phase with each other. The master/slave configuration looks to have the best potential, though you'll need to pump the master TX DMA, no experience here with Rx only configuration in that regard.

[sburr]

Posted on February 13, 2015 at 08:08 Did you actually get this to work, I'm facing a similar problem with dual ADC's

[Tesla DeLorean]

Posted on February 13, 2015 at 17:32

Did you actually get this to work, I'm facing a similar problem with dual ADC's

And what to this point have you actually tried to prototype/test in terms of topology?