SPMCK16Z4MPV16 datasheet(262/500 Pages) FREESCALE

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MULTICHANNEL COMMUNICATION INTERFACE

M68HC16 Z SERIES

10-22

USER’S MANUAL

In some applications, software overhead can cause a bit-time of logic level one to oc-

cur between frames. This bit-time does not affect content, but if it occurs after a frame

of ones when short detection is enabled, the receiver flags an idle line.

When the ILIE bit in SCCR1 is set, an interrupt request is generated when the IDLE

flag is set. The flag is cleared by reading SCSR and SCDR in sequence. IDLE is not

set again until after at least one frame has been received (RDRF = 1). This prevents

an extended idle interval from causing more than one interrupt.

10.4.5.8 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 SCCR1. While RWU

is set, receiver status flags and interrupts are disabled. Although the CPU32 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 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. For idle-line wake-up to work, there must be a min-

imum of one frame of idle line between transmissions. There must be no idle time be-

tween 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.

10.4.5.9 Internal Loop

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.

Freescale Semiconductor, Inc.

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SPMCK16Z4MPV16 Datasheet(PDF) 262 Page - Freescale Semiconductor, Inc

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