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.
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 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
24
MPC89x515A Data Sheet
MEGAWIN
MEGAWIN [ MEGAWIN TECHNOLOGY CO., LTD ]
