MOTOROLA
Chapter 15. Queued Serial Multi-Channel Module
15-63
SCI Queue Operation
15.7.7.10 Receiver Wake-Up
The receiver wake-up function allows a transmitting device to direct a transmission to a
single receiver or to a group of receivers by sending an address frame at the start of a
message. Hardware activates each receiver in a system under certain conditions. Resident
software must process address information and enable or disable receiver operation.
A receiver is placed in wake-up mode by setting the RWU bit in SCCxR1. While RWU is
set, receiver status flags and interrupts are disabled. Although the software can clear RWU,
it is normally cleared by hardware during wake-up.
The WAKE bit in SCCxR1 determines which type of wake-up is used. When WAKE = 0,
idle-line wake-up is selected. When WAKE = 1, address-mark wake-up is selected. Both
types require a software-based device addressing and recognition scheme.
Idle-line wake-up allows a receiver to sleep until an idle line is detected. When an idle line
is detected, the receiver clears RWU and wakes up. The receiver waits for the first frame of
the next transmission. The data frame is received normally, transferred to the RDRx, and
the RDRF flag is set. If software does not recognize the address, it can set RWU and put the
receiver back to sleep. For idle-line wake-up to work, there must be a minimum of one
frame of idle line between transmissions. There must be no idle time between frames within
a transmission.
Address mark wake-up uses a special frame format to wake up the receiver. When the MSB
of an address-mark frame is set, that frame contains address information. The first frame of
each transmission must be an address frame. When the MSB of a frame is set, the receiver
clears RWU and wakes up. The data frame is received normally, transferred to the RDRx,
and the RDRF flag is set. If software does not recognize the address, it can set RWU and
put the receiver back to sleep. Address mark wake-up allows idle time between frames and
eliminates idle time between transmissions. However, there is a loss of efficiency because
of an additional bit-time per frame.
15.7.7.11 Internal Loop Mode
The LOOPS bit in SCCxR1 controls a feedback path in the data serial shifter. When
LOOPS is set, the SCI transmitter output is fed back into the receive serial shifter. TXD is
asserted (idle line). Both transmitter and receiver must be enabled before entering loop
mode.
15.8 SCI Queue Operation
15.8.1
Queue Operation of SCI1 for Transmit and Receive
The SCI1 serial module allows for queueing on transmit and receive data frames. In the
standard mode, in which the queue is disabled, the SCI1 operates as previously defined (i.e.,