Mode2

An 11-bit data is serially transmitted through TXD or received through RXD. The frame data

includes a start bit (0), 8 data bits, a programmable 9th bit and a stop bit (1). On transmit, the

9th data bit comes from TB8 in SFR SCON. On receive, the 9th data bit 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

Mode3

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

2

SMOD

32

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 bit 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):

Bit-7

Bit-6

Bit-5

Bit-4

Bit-3

Bit-2

Bit-1

Bit-0

SM0/FE

SM1

SM2

REN

TB8

RB8

TI

RI

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

cleared by valid frames, but should be cleared by software. The SMOD0 (PCON.6) bit must be set to

enable access to the FE bit.

{ 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

Baud Rate (for Mode 3)

=

(Timer-2 overflow rate)

16

or =

24

MPC89x53A Data Sheet

MEGAWIN