HT85F2270 datasheet(205/226 Pages) HOLTEK

205 / 226 page

Rev. 1.00

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Standard 8051 8-Bit Flash MCU

HT85F2260/HT85F2270/HT85F2280

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

�ode 0

8-bit shift register

fSYS/1�

S�nchronous

None

�ode 1

8-bit UART

Variable

As�nchronous

1 Start� 1 Stop

�ode �

9-bit UART

SP0CLK/�� or SP0CLK/64

As�nchronous

1 Start� 1 Stop

�ode �

9-bit UART

Variable

As�nchronous

1 Start� 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 fSYS/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 fSYS/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.

RX D0

(D at a ou t)

Da ta T ra ns mi t Ti mi ng Di ag ra m

TX D0

(C lo ck ou t)

RX D0

(D at a in )

Da ta R ecer i ve Ti mi ng D ia gr am

TX D0

(C lo ck ou t)

UART0 Mode 0 Timing Diagram

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