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DS90UB954-Q1: The issue of i2c pass through on DS90UB954-Q1 through with DS90UB953 to camera sensor

Part Number: DS90UB954-Q1

Hi,

     We have a working settings on BC frequency 50Mbps. Due to the ESD ,we would like to change data rate to 25Mbps. After changing to use 25Mbps, we measured the i2c packets and found the 953 did not send out the i2c payloads to camera sensor,only measure the camera sensor slave address from 953 i2c pin.We also measured 954,the i2c payload is normally sent to 954.

     The BC 50Mbps frequncy work settings are as following

;TI954 registers' init:
;Addr Register Value
60 01 01 ;reset0
SL 200
60 4C 01
60 BA 80
60 7C 00
60 B9 3F
60 D5 E0
60 42 71
60 41 E0
60 33 21
60 58 5E
60 5C 32
60 5D 6C
60 65 6C
60 20 20
60 B0 14 ;CMLOUT
60 B1 00
60 B2 80
60 B1 03
60 B2 28
60 B1 04
60 B2 28
60 B1 02
60 B2 20
60 B0 04
60 B1 0F
60 B2 01
60 B1 10
60 B2 02


;TI953 registers' init:
;Addr Register Value
32 02 13
32 06 41
32 07 28
32 0B 7F
32 0C 7F
32 0E 60
32 0D 07

   For the ESD, we changed 954 register 0x58 to 0x5D and 953 register 0x06 to 0x21 for changing BC frequency to 25Mbps. After changing that, the i2c payloads cannot be passed through 954/953 to camera sensor. Is there any other registers should be adjust? We have another platform with the same 25Mbps settings,it can work fine.

regards,

Sean

  

  • Hi Sean,

    1) It seems your original 953/954 setup is in Synchronous Mode, with a FC rate of about 4Gbps and a BC rate of 50Mbps. And you had a stable LOCK, with no issues sending I2C commands to the remote I2C bus. Can you confirm if this is correct?

    If so, then in order to switch to a 25Mbps BC rate, you would first need to enable RX_WRITE_PORT_0 on the 954 (reg 0x4C = 0x01) and then set the Back Channel to 25Mbps (reg 0x58 = 0x5D). 

    You do not need to write to reg 0x06 in the 953 device, to configure the BC rate. In Synchronous mode, the 953 will take whatever BC frequency the DES sends and use it to drive the Forward Channel. Reg 0x06 in the 953 device is used to configure the CLKOUT signal.

    2) After switching to the 25Mbps BC rate, can you confirm that LOCK is still stable and HIGH, by reading register 0x4D in the 954 device.

    Some additional info:

    Frequency of the REFCLK sent to the SER in Synchronous mode is half the BC bit rate, so if the BC is set to 25Mbps, then the REFCLK to the SER is about 12.5MHz. You can use Table 7-6 in the 953 datasheet to calculate the new data rates, if you lower the BC rate.

    Make sure that your system still meets the CSI Bandwidth and CLK_OUT specs, with the new BC rate.

    Best,

    Justin Phan