DSP56857 datasheet(256/662 Pages) FREESCALE

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Functional Description

5685X Digital Signal Controller User Manual, Rev. 4

10-20

Freescale Semiconductor

Address Mark Wake Up allows messages to contain preambles but it requires the MSB to be

reserved for use in address frames.

Note:

With the WAKE bit clear, setting the RWU bit after the RXD pin has been idle can

cause the receiver to wake up immediately.

10.6.5 Single Wire Operation

Normally, the SCI uses two pins for transmitting and receiving. In the single wire operation, the

RXD pin is disconnected from the SCI and is available as a General Purpose I/O (GPIO) pin. The

SCI uses the TXD pin for both receiving and transmitting.

Setting the TE bit in the SCI Control Register (SCICR) configures TXD as the output for

transmitted data. Clearing the TE bit configures TXD as the input for received data.

Figure 10-15. Single Wire Operation (LOOP = 1, RSRC = 1)

Enable single wire operation by setting the LOOP bit and the Receiver Source (RSRC) bit in the

SCI Control Register (SCICR). Setting the LOOP bit disables the path from the RXD pin to the

receiver. Setting the RSRC bit connects the receiver input to the output of the TXD pin driver.

10.6.6 Loop Operation

In Loop operation the transmitter output goes to the receiver input. The RXD pin is disconnected

from the SCI and is available as a GPIO pin.

Setting the TE bit in the SCI Control Register (SCICR) connects the transmitter output to the

TXD pin. Clearing the TE bit disconnects the transmitter output from the TXD pin.

Figure 10-16. Loop Operation (LOOP = 1, RSRC = 0)

TXD

RXD

Transmitter

Receiver

General

Purpose I/O

TXD

RXD

General

Purpose I/O

Transmitter

Receiver

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