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Synchronization issue of multiple ADE7913

Question asked by Ivan-Rusov Employee on Oct 13, 2014
Latest reply on Oct 16, 2014 by Ivan-Rusov

Hi,

 

I have an issue with synchronization of 3x ADE7913.

 

I use uC with SPI clocks 6 MHz or 3 MHz. I can't use 6 MHz SPI clocks due to ADE7913 has 5.6 MHz SCLK limit. So I use 3 MHz for SCLK.

 

When 3x ADE7913 are used I can't read all data during 125 us (8 kSPS) time slot. I read data by using SPI Read Operation in Burst Mode (128 bit per ADE7913). For my configuration reading time is 3*(1/3000000Hz)*128bit=128 us. 128 us > 125 us (8 kSPS) and I can't read data from 3x ADE7913 during 125 us time slot.

 

When I decrease sampling rate by factor 2 (4 kSPS or 250 us for reading data) I get some issues.

 

1st issue. CRC issue.

I get wrong CRC when I use any other than 8 kSPS sampling rate. For example, when 4 kSPS is used, CRC is correct only when reading time is close to the end of sampling period.

Below you can see timing diagrams (for 8kHz and 4kHz).

Channel 1 (yellow) - DREADY from ADE7913.

Channel 2 (red) - NCS from uC. Here you can estimate data reading start time and data reading duration.

Channel 3 (blue) - CRC error. Active High level is set when ADE7913 CRC and calculated CRC are not equal.

 

8kHz (8kSPS):

ws64xs-a1_8kHz.png

ws64xs-a4_8kHz.png

 

ws64xs-a5_8kHz.png

 

4 kHz (4 kSPS):

ws64xs-a6_4kHz.png

 

ws64xs-a10_4kHz.png

ws64xs-a11_4kHz.png

 

Could you please comment this issue?

 

2nd issue. Unsynchronized DREADY is observed when several ADE7913 are working with different sampling frequencies.

For example, if 1st ADE7913 is working at 8 kSPS and 2nd ADE7913 at 4 kSPS then DREADY signals are unsynchronized. Below you can see timing diagram.

Channel 1 (yellow) - NCS from uC. Broadcast write 0x01 to SYNC_SNAP.

Channel 2 (red) - DREADY from ADE7913 (8 kHz).

Channel 3 (blue) - DREADY from ADE7913 (4 kHz).

ws64xs-a13_4_8kHz.png

How could 8 kHz ADE7913 and 4 kHz ADE7913 work synchronously? If yes, could you provide me correct method? Thank you in advance.

 

If you need more information please contact me.

 

Regards,

Ivan

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