MC68HC16Z1CPV16 Datasheet, PDF (240/500 Pages) Freescale Semiconductor, Inc – Symbols and Operators, CPU16 Register Mnemonics

Freescale Semiconductor, Inc.
A receiver is placed in wake-up mode by setting the RWU bit in SCCR1. While RWU
is set, receiver status flags and interrupts are disabled. Although the CPU16 can clear
RWU, it is normally cleared by hardware during wake-up.
The WAKE bit in SCCR1 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 byte is received normally, transferred to 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. 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 byte is received normally, trans-
ferred to the RDR, and the RDRF flag is set. If software does not recognize the ad-
dress, 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. How-
ever, there is a loss of efficiency because of an additional bit-time per frame.
9.4.3.9 Internal Loop Mode
The LOOPS bit in SCCR1 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.
9-30
QUEUED SERIAL MODULE
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