MPC89L51AF 参数 Datasheet PDF下载

Mode2

An 11-bits data is serially transmitted through

TXD

or received through

RXD.

The frame data

includes a start bits (0), 8 data bits, a programmable 9

th

bits and a stop bits (1). On transmit, the

9

th

data bits comes from

TB8

in SFR

SCON.

On receive, the 9

th

data bits goes into

RB8

in

SCON.

The baud rate is programmable, and permitted to be set either 1/32 or 1/64 the oscillator

frequency.

Baud Rate (for Mode 2)

=

2

SMOD

64

X

F

osc

Mode3

Mode 3 is the same as mode 2 except the baud rate is variable.

Baud Rate (for Mode 3)

=

2

SMOD

32

X

(Timer-1 overflow rate)

or =

(Timer-2 overflow rate)

16

In all four modes, transmission is initiated by any instruction that uses SBUF as a destination

register. Reception is initiated in mode 0 by the condition

RI

=

0

and

REN

=

1.

Reception is

initiated in the other modes by the incoming start bits with

1-to-0

transition if

REN=1.

There are several SFR related to serial port configuration described as following.

SFR:

SCON

(Serial

Port Control):

Bits-7

SM0/FE

Bits-6

SM1

Bits-5

SM2

Bits-4

REN

Bits-3

TB8

Bits-2

RB8

Bits-1

TI

Bits-0

RI

FE:

Frame Error bits. This bits is set by the receiver when an invalid stop bits is detected. The FE bits is not

cleared by valid frames, but should be cleared by software. The

SMOD0 (PCON.6)

bits must be set to

enable access to the FE bits.

{ SM0, SM1 }:

Used to set operating mode of the serial port. It is enabled to access by clearing SMOD0.

{

0, 0

} := set the serial port operate under Mode 0

{

0, 1

} := set the serial port operate under Mode 1

{

1, 0

} := set the serial port operate under Mode 2

{

1, 1

} := set the serial port operate under Mode 3

24

MPC89x51A Data Sheet

MEGAWIN