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TLC542: Can the TLC1542 sub?

newell
Prodigy 100 points
Part Number: TLC542
Other Parts Discussed in Thread: TLC1542, TLV2556, TLV2553, TLV2543, TLC2543

Can I use the active TLC1542 to sub for the last-time-buy TLC542?

I don't want to mod firmware, so the '1542 would need to output 8 good bits and it wouldn't get enough SPI clock bits to output all 10 bits. (We do not use the EOC output on pin 19.)

thanks!

  • 0
    TI__Guru**** 181981 points
    Hi newell,

    Unfortunately no, the TLC1542 sample mechanism needs 6 clock cycles to sample properly where the TLC542 only needs 4 (see page 2 in the TLC542 datasheet versus Figure 9 in the TLC1542 document). With only 8 SCLKs applied instead of the 10 needed for the TLC1542, you won't fulfill the sample time requirement.
  • 0 in reply to Tom Hendrick
    Prodigy 100 points

    Figures.

    I was hopeful we could 'short cycle' the state machine and get 7 or 8 valid bits out, but I guess not.

    Any suggestions on a replacement? (I guess if we're forced to spin the board, maybe a microcontroller could be programmed to act like the '542.)

  • 0 in reply to newell
    TI__Guru**** 181981 points

    Hi newell,

    We have other 11 channel parts, but they are all 10-12 bits and have similar sampling mechanisms to the TLC1542, you can't really short cycle them.  Can you modify the firmware to get two more SCLK cycles?  

  • 0 in reply to Tom Hendrick
    Prodigy 100 points

    We could, but it doesn't solve the problem.

    That sort of hardware change would break the firmware that's already in the field. (Our customers have the ability to load different applications into our hardware.)

  • 0 in reply to newell
    Prodigy 100 points

    Hey, what about the TLV2556? It appears to offer the same pinout and an 8 bit mode. We might be able to modify the bootloader (which runs before the main firmware) to config it to 8 bit mode at boot, then the old firmware could treat it as a TLC542.

    This one looks promising.

    My backup plan is a minor board spin and an AVR microcontroller simulating the TLC542 interface.

  • 0 in reply to newell
    TI__Guru**** 181981 points

    Hi newell!

    Figure 4 in the TLV2556 data sheet definitely makes this look like a viable solution.  That picture shows only 4 clocks through the sample cycle.  I can get you some sample devices to try if you'd like to see if they work with your existing firmware.

  • 0 in reply to Tom Hendrick
    Prodigy 100 points

    After reading the datasheet again, I don't think the TLV2556 will work. I can probably get CFGR2 configured in the bootloader and then the main app wouldn't touch it, but the problem turns out to be CFGR1. Looks like every single conversion needs to specify both the channel (no problem there--same as the TLC542), but also the output data format. All the existing firmware transmits 0 for the lower nibble, and it appears that would put the interface in 12 bit mode. Foiled by a single bit!

    The TLC2543, TLV2553, and TLV2543 all appear to share the same serial command structure, so no help there, either.

  • 0 in reply to newell
    TI__Guru**** 181981 points

    Bummer!  Sorry - I missed that too...