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
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 SFRs related to serial port configuration described as following.
SFR: SCON (Serial 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 bit must be set to enable access
to the FE bit.
{ SM0, SM1 }:= Used to set operating mode of the serial port.
{ 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
SM2:= Enable the automatic address recognition feature in mode 2 and 3.
If SM2=1, RI will not be set unless the received 9th data bit is 1, indicating an address, and
the received byte is a Given or Broadcast address. In mode1, if SM2=1, RI will not be set
unless a valid stop Bit was received, and the received byte is a Given or Broadcast
address.
REN:= Enable the serial port reception.
0:= (default)
Disable the serial port reception.
1:=
Enable the serial port reception.
TB8:= The 9th data bit, which will be transmitted in Mode 2 and Mode 3.
RB8:= In mode 2 and 3, the received 9th data bit will be put into this bit.
TI:= Transmitting done flag. After a transmitting has been finished, the hardware will set this bit.
RI:= Receive done flag. After reception has been finished, the hardware will set this bit.
36
MPC82x54A Data Sheet
MEGAWIN
MEGAWIN [ MEGAWIN TECHNOLOGY CO., LTD ]
