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AD7175-8 Using Single Ended Inputs - Only able to read Odd Numbered Channels

Question asked by redplanet on Nov 2, 2017
Latest reply on Nov 3, 2017 by redplanet

Dear EngineerZone community,

 

The device presenting an issue is AD7175-8 interfaced to an Atmel Sam4S via SPI communications.  It is configured to read single ended data from channels 0 through 9 at a sample rate of 59.9Hz. 

 

All channels use the same Setup_Config_0 configured as 0x0300 => Unipolar, AINBUF+ enabled, External Reference.  Filter_Config_0 is configured as 0x020F => Sinc3, 59.92 S/s  

Offset and Gain are unchanged from default.

 

A read of all channels 0 through 9, along with respective status byte for each channel, indicates only odd number channel acquisition data are being read.  Modifying the code to only read even channels results in odd channel data read back. 

 

Having read back the setup registers over SPI, fairly confident the setup is correct:  

Read Ch 0 Map, now 0x8016  // channel enabled
Read Ch 1 Map, now 0x0036  // channel disabled
Read Ch 2 Map, now 0x8056
Read Ch 3 Map, now 0x0076
Read Ch 4 Map, now 0x8096
Read Ch 5 Map, now 0x00b6
Read Ch 6 Map, now 0x80d6
Read Ch 7 Map, now 0x00f6
Read Ch 8 Map, now 0x8116
Read Ch 9 Map, now 0x0136
Read Ch 10 Map, now 0x0156
Read Ch 11 Map, now 0x0176

 

Whether continually reading or performing a read on just a single channel, the status byte received with the data indicates an odd numbered channel. 

Status Byte (I know it indicates an ADC_ERROR.  This is due to no input voltage, inputs float to small negative V.)

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47 A/D conversion, now 0.000000
43 A/D conversion, now 0.000000
49 A/D conversion, now 0.000000
45 A/D conversion, now 0.000000
49 A/D conversion, now 0.000000
43 A/D conversion, now 0.000000
49 A/D conversion, now 0.000000
45 A/D conversion, now 0.000000
41 A/D conversion, now 0.000000

 

Modification of the code to only read channel 0 results in readback with status byte indicating channel 1.

 

Thank you for any advice and/or direction.

 

Mark

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