
Functional Description
MOTOROLA
Serial Communications Interface (SCI)
10-19
Preliminary
10
The maximum percent difference between the receiver count and the transmitter count of a
fast 9-bit character with no errors is:
10.6.4.8 Receiver Wake Up
In order for the SCI to ignore transmissions intended only for other receivers in
multiple-receiver systems, the receiver can be put into a standby state. Setting the
Receiver Wake Up (RWU) bit in the SCI Control Register (SCICR) puts the receiver into
a standby state while receiver interrupts are disabled.
The transmitting device can address messages to selected receivers by including
addressing information in the initial frame or frames of each message.
The WAKE bit in the SCI Control Register (SCICR) determines how the SCI is brought
out of the standby state to process an incoming message. The WAKE bit enables either
idle line wake up or address mark wake up:
Idle Input Line Wake Up (WAKE = 0)—In this wake up 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
following frames. 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 preamble appears on the RXD pin.
Idle line wake up requires messages be separated by at least one preamble and no
message contains preambles.
The preamble waking a receiver does not set the receiver Idle (IDLE) bit or the
Receive Data Register Full (RDRF) flag.
Address Mark Wake up (WAKE = 1)—In this wake up method, a logic one in the
Most Significant Bit (MSB) position of a frame clears the RWU bit and wakes up the
SCI. The logic one 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.
170
176
–
170
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100
×
3.53%
=