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LMH1228: SPI timing for register mask in register command syntax

Takahiro Saito
Expert 5465 points
Part Number: LMH1228


Hi team,

In order to write the register, I believe it needs SPI length of 25bits because the register command syntax is 25bits in total (RAW + address + contents + mask=1bit+8bit+8bit+8bit). But, the datasheet describes SPI timing for only 17bit length.  So, there is no location for "register mask". How should I locate the register mask? Could you show me the SPI timing for SPI length of 25bits to confirm the SPI timing of comlete register command syntax?

Regards,

Saito 

  • 0
    TI__Guru* 93570 points

    Hi Saito-San,

    RAW and register mask are used in programming guide for LMH1228, other LMH12xx, and ethernet devices. This just shows command syntax/format and is not related to the actual electrical interface. Interface is 17-bits as noted in the data sheet. Please also view the following video describing SPI operation in more details:

    https://training.ti.com/spi-access-using-fpga-or-asic-using-lmh12xx-12g-sdi-devices

    Regards,,,Nasser

  • 0 in reply to Nasser Mohammadi
    TI__Expert 5465 points

    Hi Nasser-san,

    Thank you for your answer.

    So, is the following procedure correct to input command to LMH1228?

    1. Write Address(8bits) and Data(8bits) with R/W bit set to 1.
    2. De-assert SS_N signal.
    3. Write Mask bits.
    4. Deassert SS_N signal

    Regards,

    Saito

  • 0 in reply to Takahiro Saito
    TI__Guru* 93570 points

    Hi Saito-San,

    There are different ways you can change register content through SPI interface.

    1a). The simplest way is to use register default setting as noted in the programming guide.

    1b). Then change bits that is required.

    1c). Use 17-bits write format as shown in the data sheet to change a register content.

    You can also do the followings - without reading default settings from programming guide:

    2a). Read register settings, 34-bits, as noted in the data sheet.

    2b). On FPGA or micro-controller, change register bits as needed.

    2c). Write register settings ,17-bit, using format noted in the data sheet.

    Regards,, Nasser