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SH79F3283
90
8.5 EUART
8.5.1 Feature
The SH79F3283 has two enhanced EUART (EUART0/1) which are compatible with the conventional 8051
The EUART0 baud rate can be selected from the divided clock of the system clock, or Timer4/2 overflow rate, The
Euart1 baud rate generator is an 15-bit up-counting timer
Enhancements over the standard 8051 the EUART include Framing Error detection and automatic address
recognition
The EUART can be operated in four modes
8.5.2 EUART0
The EUART0 can be operated in 4 modes. Users must initialize the SCON before any communication can take place. This
involves selection of the Mode and the baud rate. The Timer4/2 should also be initialized if the mode 1 or the mode 3 is used.
In all of the 4 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. This will generate a clock on the TXD0 pin and shift in 8 bits on the RxD0 pin.
Reception is initiated in the other modes by the input start bit if REN = 1. The external transmitter will start the communication
by transmitting the start bit.
EUART Mode Summary
SM0
SM1
Mode
Type
Baud Rate
Frame Size Start Bit Stop Bit
9th bit
0
0
0
Synch
f
SYS
/(4 or 12)
8 bits
NO
NO
None
0
1
1
Asynch
Timer 4 or 2 overflow rate/(16 or 32)
10 bits
1
1
None
1
0
2
Asynch
f
SYS
/(32 or 64)
11 bits
1
1
0, 1
1
1
3
Asynch
Timer 4 or 2 overflow rate/(16 or 32)
11 bits
1
1
0, 1
Mode0: Synchronous Mode, Half duplex
This mode provides synchronous communication with external devices. In this mode serial data is transmitted and received on
the RXD pin. TXD is used to output the shift clock. The TXD clock is provided by the 3283 whether the device is transmitting or
receiving. Therefore, this mode is a half duplex mode of serial communication. In this mode, 8 bits are transmitted or received
per frame. The LSB is transmitted / received first.
The baud rate is programmable to either 1/12 or 1/4 of the system clock. This baud rate is determined in the SM2 bit
(SCON.5). When this bit is set to 0, the serial port runs at 1/12 of the system clock. When set to 1, the serial port runs at 1/4 of
the system clock. The only difference from standard 8051 is that SH79F3283 in the mode 0 has variable baud rate.
The functional block diagram is shown below. Data enters and exits the serial port on the RXD pin. The TXD pin is used to
output the SHIFT CLOCK. The SHIFT CLOCK is used to shift data into and out of the SH79F3283.
12
4
SERIAL
CONTROLLER
TX CLOCK
TX START
TX SHIFT
TI
RI
SHIFT
CLOCK
RX CLOCK
LOAD SBUF
RX START
RX SHIFT
Transmit Shift Register
RXD
Serial Port Interrupt
TXD
RI
REN
PARIN
LOAD
CLOCK
SOUT
CLOCK
SIN
PAROUT
RXD
SBUF
Read SBUF
Receive Shift Register
Internal
Data Bus
Write to
SBUF
1
0
SBUF
÷
÷
System Clock
SM2