
Rev. 1.00
�04 of ���
�an�a�� 1�� �01�
Standard 8051 8-Bit Flash MCU
HT85F2260/HT85F2270/HT85F2280
UART Serial Interfaces – UART0 and UART1
UART0 Operating Modes
UART0 provides four operation modes, selected by the SM1 and SM0 bits in the S0CON register.
There are one synchronous and three asynchronous modes, offering different baud rates and
functional options. The following table illustrates the different operational mode list. When a
transmit/receive data transfer operation has completed, a transmit/receive interrupt will take place
and the interrupt request bit, TI0 or RI0, will be set high.
UART0 Operating Modes
Mode
Mode Name
Baud Rate
Synchronisation
Start/Stop Bits
Mode 0
8-bit shift �egiste�
f
SYS
/1�
S�nch�ono�s
None
Mode 1
8-bit UART
Va�iable
As�nch�ono�s
1 Sta�t� 1 Stop
Mode �
9-bit UART
SP0CLK/3� o� SP0CLK/64
As�nch�ono�s
1 Sta�t� 1 Stop
Mode 3
9-bit UART
Va�iable
As�nch�ono�s
1 Sta�t� 1 Stop
Mode 0
Mode 0 is an integrated half-duplex synchronous serial communication interface. The 8 bits of
data are communicated via the RXD0 pin while the TXD0 pin provides the shift clock for this
communication. The data will then be transferred to the Transmit Shift Register from where it will
be shifted out, LSB first, onto the RXD0 pin at a fixed Baud rate of f
SYS
/12. The Transmission is
started by writing a data into the S0BUF register.
Data to be received by the UART is accepted on the external RXD0 pin, from where it is shifted in,
LSB first, to the Receiver Shift Register at a fixed Baud rate of f
SYS
/12. The reception is started by
setting the REN0 bit in the S0CON register to “1”. When the shift register is full, the data will then
be transferred from the shift register to the internal S0BUF register, where it is buffered and can be
manipulated by the application program.
UART0 Mode 0 Timing Diagram