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 9th bits and a stop bits (1). On transmit, the
9th data bits comes from TB8 in SFR SCON. On receive, the 9th 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.
2 SMOD
X Fosc
Baud Rate (for Mode 2) =
64
Mode3
Mode 3 is the same as mode 2 except the baud rate is variable.
2 SMOD
Baud Rate (for Mode 3) =
X
(Timer-1 overflow rate)
32
(Timer-2 overflow rate)
or =
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
Bits-6
Bits-5
Bits-4
Bits-3
Bits-2
Bits-1
Bits-0
SM0/FE
SM1
SM2
REN
TB8
RB8
TI
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
MEGAWIN [ MEGAWIN TECHNOLOGY CO., LTD ]
