AT2LP Pull-Down resistor of DD7 port

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    Question: According to AT2LP datasheet, 1K ohm pull-down resistor is required on DD7 pin. Why the pull-down is needed?



    when AT2LP Host through it's initialization routine at power-up it determines if the device is a master or a slave device and because the ATA/ATAPI spec requires that there is no pull-up on DD7 and a pull-down resistor on the device.

    Since in this routine we look at this bit and expect it must be pulled down. The ATA/ATAPI spec says to use a 10K resistor but a 10K resistor might be not sufficient to get a low indication. If the pull-down resistor is not there, the bridge chip could think that the attached device is a master when it is a slave or could think that it is a slave when it is really a master. Because of this you should be safe and add the pull-down resistor. We recommend the DD7 pin should be connected with a 1K ohm pull-down resistor.