3221 RS-232 driver/receiver auto-powerdown mode

Meredith Lecocke

Other Parts Discussed in Thread: SN75C3221, SN65C3221

Hello -

In the SN65C3221/SN75C3221 datasheet, the "auto-powerdown" (low power/sleep) mode is described like this:

"During this mode of operation, if the devices do not sense a valid RS-232 signal on the receiver input, the driver output is disabled."

Does this mean that a signal on the RX line is the ONLY way auto-powerdown mode can be exited? In other words, if the chip enters auto-powerdown mode and disables the driver output, does not receive any signal on the receiver, but then a signal is supplied to the TX line, will it power up the driver and send out the message?

Thank you for your help -

over 13 years ago

0 Ron Michallick over 13 years ago

TI__Guru*** 149776 points

Hello Meredith,

The second way to exit "auto-power down" is to apply a logic high to the "FORCEON" input.
It will take about 30uS (Data sheet typical say 100uS) between exiting "auto-power down" before the driver will be ready to send.
The charge pump is refilling during this time.

Regards,
Ron Michallick

0 Ron Michallick over 13 years ago in reply to Ron Michallick

TI__Guru*** 149776 points

Meredith,

I just noticed that the typical spec is supply enable time is 100uS on page 6 of the data sheet.

Ron

0 Meredith Lecocke over 13 years ago in reply to Ron Michallick

Prodigy 20 points

Ron, thanks for your responses. So simply applying a signal to the TX line is not sufficient to exit powerdown mode; I must assert FORCEON. Correct?

Thanks for your help!

- M

0 Ron Michallick over 13 years ago in reply to Meredith Lecocke

TI__Guru*** 149776 points

Your understanding is correct.

Ron

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3221 RS-232 driver/receiver auto-powerdown mode