Universal Asynchronous Serial Port (UART)
The serial port of MPC82x54A is duplex. It can transmit and receive simultaneously. The
receiving and transmitting of the serial port share the same SFR
SBUF,
but actually there are
two SBUF registers implemented in the chip. One is for transmitting and the other is for
receiving. The serial port can be operated in 4 different modes.
Mode 0
Generally, this mode purely is used to extend the I/O features of this device.
Operating under this mode, the device receives the serial data or transmits the serial data via
pin RXD while there is a clock stream shifted via pin TXD which makes convenient for external
synchronization. An 8-bit data is serially transmitted/received with LSB first. The baud rate is
fixed at 1/12 the oscillator frequency. If
AUXR.5
(URM0X6) is set, the baud rate is 1/2
oscillator frequency.
Mode1
A 10-bits data is serially transmitted through pin TXD or received through pin RXD. The frame
data includes a start bit (0), 8 data bits and a stop bit (1). After finishing a receiving, the device
will keep the stop bit in
RB8
which from SRF
SCON.
Baud Rate (for Mode 1)
=
2
SMOD
32
X
(Timer-1 overflow rate)
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
F
osc
MEGAWIN
MPC82x54A Data Sheet
35
MEGAWIN [ MEGAWIN TECHNOLOGY CO., LTD ]
