Can multiple AD7949 chips share a common SPI interface?

flying510

Can multiple AD7949 chips share a common SPI interface? [Copy link]

 

According to the timing requirements of the data sheet, CNV is used to start the conversion. So can it also be used as a chip select signal? Has anyone done this before? Please give me some advice.

damiaa

It won't report to three chips. If CNV is low, the chips will not output data. Their output should be high impedance. It just means that this pin has two functions: 1. Start conversion. 2. It is equivalent to chip select (not a real chip select, anyway, it does not output data, and keeps the converted data after the internal conversion, waiting to send it to you next time CNV is high). Just pay attention to the time rhythm. Remember that the data you read when CNV is high this time is the data of the last conversion. Here's another useful document for you. Different from the following documents, this is an evaluation board document with detailed instructions for using CNV: AD7942.pdf (456.54 KB, downloads: 24)

2017-4-21 16:25 上传

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CNV： Convert Input. This input pin has multiple functions. On its leading edge, CNV initiates the conversions and selects the interface mode of the part: chain mode or CS mode. In CS mode, CNV enables the SDO pin when low. In chain mode, the data should be read when CNV is high.

damiaa

AD7949_cn.pdf (753.83 KB, downloads: 17)

2017-4-21 16:01 上传

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I saw a typical usage diagram in it that the chip select is connected. This should be OK, because CNV is mainly used to start the conversion. When the level is low, the internal conversion starts, and the data input and output are not effective. And this chip seems to have SCK inside, so should SCK not be connected?

flying510

Is this the picture you are talking about? This chip select can only be used as a normal IO, not as a chip enable (working or not working). So how to deal with multiple AD7949s? If I use the same SPI, when reading data (for example, there are 3PCS), will all the data of 3PCS be reported? This is obviously not possible.

littleshrimp

Visually, it is not possible because there is no chip select pin and daisy chain is not supported. You can try digital multiplexing

flying510

You can use interrupts to get data. But this is really only a last resort when you are really short of resources:)damiaa posted on 2017-4-21 15:54 I saw a typical usage diagram that connected the chip select. This should be possible, because CNV is mainly used to start the conversion. When the low level starts the internal conversion, the data...

SCK should still be needed. The internal SCK is used for the conversion function, but the data transmission still requires a clock.

flying510

damiaa posted on 2017-4-21 16:11 It won't report three chips. If CNV is low, the chips will not output data. Their output should be high impedance. It just says that this pin has two...

ad7942 does a good job in connection, but AD7949 does not support this function. My current demand is more channels and reasonable price. AD7942 does not meet it at all. :Sad:

damiaa

flying510 posted on 2017-4-21 17:08 ad7942 does a good job in connection, but AD7949 does not support this function. My current demand is more channels and the price must be reasonable. AD7942 completely...

ADI's chips are more expensive.

suoma

One chip select per chip

strong161

Theoretically, it can definitely be shared, just add some digital circuit multiplexing!

flying510

strong161 posted on 2017-4-22 12:59 In theory, they can definitely be shared. Just add some digital circuits for reuse!

Hello, do you have any good reuse chip recommendations?

damiaa

Analog Switches