MCCIRM Freescale Semiconductor / Motorola, MCCIRM Datasheet - Page 76

• Manufacturer Part Number: MCCIRM
• Description: MCCIRM Multi-Channel Communications Interface Reference Manual
• Manufacturer: Freescale Semiconductor / Motorola

SCI Submodule
5.7.10 Receiver Wakeup
5.7.10.1 Idle-Line Wakeup
5.7.10.2 Address-Mark Wakeup
Reference Manual
76
The receiver wakeup 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. Receivers not addressed
become dormant for the remainder of the message, eliminating any
further software overhead to service the remaining characters of the
message.
Software places the receiver in wakeup mode by setting the receiver
wakeup (RWU) bit in SCCR1. While RWU is set, receiver status flags
cannot be set. For this reason idle-line detection cannot be used with
receiver wakeup. Hardware clears RWU using one of two methods:
idle-line wakeup or address-mark wakeup. (It is possible to clear RWU
with software, but this is not the normal procedure.)
The WAKE bit in SCCR1 determines which type of wakeup is used.
When WAKE = 0, idle-line wakeup is selected. When WAKE = 1,
address-mark wakeup is selected. Both types require a software-based
device addressing and recognition scheme.
Idle-line wakeup 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 byte
is received normally and transferred to the RDR, and the RDRF flag is
set. If software does not recognize the address, it can set RWU and put
the receiver back to sleep until the next idle line. This method of receiver
wakeup requires a minimum of one idle-line frame time between
messages and allows no idle time between frames in a message. The
ILT bit determines whether short or long idle-line detection is invoked.
Address-mark wakeup uses a special frame format. The first frame of
each transmission must be an address frame, indicated by a logic level
1 in the MSB. For all other characters, the MSB must equal 0.
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SCI Submodule
Multichannel Communication Interface — Rev. 1.0
MOTOROLA