PC912XDP512F0MPVR datasheet(510/1348 Pages) FREESCALE

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Chapter 11 Serial Communication Interface (S12SCIV5)

MC9S12XDP512 Data Sheet, Rev. 2.21

510

Freescale Semiconductor

11.4.6.6.1

Idle Input line Wakeup (WAKE = 0)

In this wakeup method, an idle condition on the RXD pin clears the RWU bit and wakes up the SCI. The

initial frame or frames of every message contain addressing information. All receivers evaluate the

addressing information, and receivers for which the message is addressed process the frames that follow.

Any receiver for which a message is not addressed can set its RWU bit and return to the standby state. The

RWU bit remains set and the receiver remains on standby until another idle character appears on the RXD

pin.

Idle line wakeup requires that messages be separated by at least one idle character and that no message

contains idle characters.

The idle character that wakes a receiver does not set the receiver idle bit, IDLE, or the receive data register

full ﬂag, RDRF.

The idle line type bit, ILT, determines whether the receiver begins counting logic 1s as idle character bits

after the start bit or after the stop bit. ILT is in SCI control register 1 (SCICR1).

11.4.6.6.2

Address Mark Wakeup (WAKE = 1)

In this wakeup method, a logic 1 in the most signiﬁcant bit (MSB) position of a frame clears the RWU bit

and wakes up the SCI. The logic 1 in the MSB position marks a frame as an address frame that contains

addressing information. All receivers evaluate the addressing information, and the receivers for which the

message is addressed process the frames that follow.Any receiver for which a message is not addressed can

set its RWU bit and return to the standby state. The RWU bit remains set and the receiver remains on

standby until another address frame appears on the RXD pin.

The logic 1 MSB of an address frame clears the receiver’s RWU bit before the stop bit is received and sets

the RDRF ﬂag.

Address mark wakeup allows messages to contain idle characters but requires that the MSB 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.

11.4.7

Single-Wire Operation

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

disconnected from the SCI. The SCI uses the TXD pin for both receiving and transmitting.

Figure 11-30. Single-Wire Operation (LOOPS = 1, RSRC = 1)

RXD

Transmitter

Receiver

TXD

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