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7.3 Receive Operation

During receive operations, the transmit sequence is reversed. The serial shift register receives data and transfers it to a parallel receive data register (SCDR) as a complete word. This double buffered operation allows a character to be shifted in serially while another character is already in the SCDR. An advanced data recovery scheme distinguishes valid data from noise in the serial data stream. The data input is selectively sampled to detect receive data, and a majority voting circuit determines the value and integrity of each bit.

7

M68HC11 E SERIES

SERIAL COMMUNICATIONS INTERFACE

MOTOROLA

TECHNICAL DATA

 

7-3

RECEIVER

BAUD RATE

CLOCK

DDD0

16

PD0

RxD

7

PIN BUFFER

DATA

AND CONTROL

RECOVERY

DISABLE

DRIVER

RE

M

WAKEUP

LOGIC

R8

T8

M WAKE

TDRE

TC RDRF

 

SCCR1 SCI CONTROL 1

 

SCSR

RDRF

RIE

IDLE

ILIE

 

OR

 

RIE

SCI Tx

SCI INTERRUPT

REQUESTS

REQUEST

STOP

 

 

10 (11)

- BIT

 

 

START

 

 

 

 

 

 

 

 

 

 

 

 

Rx SHIFT REGISTER

 

 

(8)

7

6

5

4

3

2

1

0

 

 

 

 

 

 

MSB

 

 

ALL ONES

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

RWU

 

8

IDLE OR NF FE

 

SCI STATUS 1

SCDR Rx BUFFER

 

(READ ONLY)

 

8

 

TCIE

 

RIE

 

ILIE

 

 

RWU

SBK

 

8

 

 

 

 

 

 

 

 

 

 

 

 

TIE

 

 

TE

RE

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

SCCR2

SCI CONTROL 2

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

INTERNAL

DATA BUS SCI RX BLOCK 2

Figure 7-2 SCI Receiver Block Diagram

MOTOROLA

SERIAL COMMUNICATIONS INTERFACE

M68HC11 E SERIES

7-4

 

TECHNICAL DATA

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