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How to synchronize two LM98722 AFEs

John Hemmings
Prodigy 40 points
Other Parts Discussed in Thread: LM98722

I am using a Contact Image Sensor (CIS) which has 6 analogue output taps.  I'm planning to use 2 AFE chips LM98722 which have 3 analogue inputs each.  I am supplying an external SH_R pulse to both AFEs and they will use the same clock.  AFE1 will generate the R,G,B pulses to drive the LEDs within the CIS.  AFE1 will then generate tag data which tells me which colour was scanned.

AFE2 needs to be synchronised to AFE1 so that it generates the correct output data, however the tag bits cannot be used since AFE2 is not generating the R,G,B pulses.  Is it possible to synchronise the 2 AFEs together in some way e.g. possibly as follows:

1) stop the SH_R pulses

2) Set up the registers

3) Apply software reset to reset the state machines

4) Lock the registers so that the state machines are now operating

5) Apply the SH_R pulses to both AFEs to start the 2 off in synchronism

Thanks in advance

John Hemmings

  • 0
    TI__Mastermind 22825 points
    Hi John,
    It should be possible to synchronize the LM98722 AFEs as you are intending. You will need to make sure that the SH_R input meets setup and hold timing with the applied INCLK of each device. This will be easier to do if the INCLK is at pixel sampling rate rather than at the internal ADC rate of the AFEs. See the SH_R Setup and Hold times (2ns typical) in section 6.6, and Figure 40 in section 7.4.15.2.

    You should set both AFEs up the same way, but just disable the LED lighting control outputs on the second AFE. That way they will both be able to include the color information in the data stream from both AFEs.

    If you are using the "3 lines in sequence" feature to control the lamp timing, you will need to configure the CB bits in the data stream to include the Line# lsb and msb. See Table 12 in section 7.4.17.

    Regards,
    Hooman
  • 0 in reply to Hooman Hashemi
    Prodigy 40 points

    Thanks Hooman

    We will set the INCLK to pixel sampling rate and guarantee the setup and hold times for SH_R.  Also we will add the Line# lsb and msb in the data stream for AFE2.

    Regards

    John