HT85F2270 datasheet(214/226 Pages) HOLTEK

214 / 226 page

Rev. 1.00

�14 of ��6

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Standard 8051 8-Bit Flash MCU

HT85F2260/HT85F2270/HT85F2280

UART1 Operating Modes

UART1 provides two operational modes, selected by the SM bit in the S1CON register. There are

two asynchronous modes, offering different baud rates and functional options. The following table

illustrates the different operational mode list. When the transmit/receive data process is complete,

the transmit/receive interrupt will take place and the interrupt request bit, TI1 or RI1, will be set

high.

UART1 Operating Modes

SM bit

Mode

Mode Name

Baud Rate

Synchronisation

Start/Stop Bits

�ode B

8-bit UART

Variable

As�nchronous

1 Start� 1 Stop

�ode A

9-bit UART

Variable

As�nchronous

1 Start� 1 Stop

Mode A

Mode A is an integrated full-duplex asynchronous serial communication interface. The 9 bits

of data are received via the RXD1 pin while the TXD1 pin provides the data transmit for this

communication. The data will then be transferred to the Transmit Shift Register from where it

will be shifted out onto the TXD1 pin by the UART1 Baud rate generator. The internal Baud rate

generator is enabled/disabled by the BD1 bit of the SBRCON register. The S1RELL/S1RELH

registers must be used to setup the Baud rate generator.

Data transmission is started by writing to the S1BUF register. The TXD1 pin outputs the serial

data. The first bit transmitted is a start bit, always “0”, and then 9 bits of data where the 9th bit is

taken from the TB81 bit of the S1CON register, after which a stop bit, always “1”, is transmitted.

Data to be received by the UART1 is accepted on the external RXD1 pin. When reception starts,

the UART1 synchronises with the falling edge detected by the RXD1 pin. Input data is available

after one byte of data is complete in the S1BUF register, and the ninth bit is available as the RB81

bit in the S1CON register. During the reception process, the S1BUF data and the RB81 bit will

remain unchanged until the process is complete.

St ar t Bi t

D 0

D 1

D 2

D 3

D 4

D 5

D 6

D 7

St op Bi t

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

TX D1

(D at a ou t)

B aud R at e

cl oc k

St ar t Bi t

D 0

D 1

D 2

D 3

D 4

D 5

D 6

D 7

St op Bi t

Da ta R ecei ve Ti mi ng D ia gr am

RX D1

(D at a in )

Sa mp li ng R at e

TB 81

RB 81

UART1 Mode A Timing Diagram

HT85F2270 Datasheet(PDF) 214 Page - Holtek Semiconductor Inc

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