HT85F2270 datasheet(206/226 Pages) HOLTEK

206 / 226 page

Rev. 1.00

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Standard 8051 8-Bit Flash MCU

HT85F2260/HT85F2270/HT85F2280

Mode 1

Mode 1 is an integrated full-duplex asynchronous serial communication interface with a variable

baud rate. The 8 bits of data are received via the RXD0 pin while the TXD0 pin is the data transmit

pin for this communication mode. For data reception, data received on the RXD0 pin will be

shifted into the Receive Shift Register by the Baud rate generator. For data transmission, data in

the Transmit Shift Register will be shifted out onto the TXD0 pin by the Baud rate generator. The

Baud rate frequency is selected by the BD bit in the SBRCON register to be either sourced from the

Timer1 overflow or to be setup by the S0RELL/S0RELH registers. In addition, the Baud rate can

be doubled using the SMOD bit in the PCON register.

Data transmission is started by writing to the S0BUF register. The TXD0 pin outputs the serial

data. The first bit transmitted is a start bit, always “0”, then 8 bits of data, after which a stop bit,

always “1”, is transmitted.

Data to be received by the UART is accepted on the external RXD0 pin. When reception starts, the

UART0 synchronises with the falling edge detected by the RXD0 pin. Input data is available after

one byte of data is complete in the S0BUF register and the value of the STOP bit is available as the

RB80 flag in the S0CON register. During the reception process, the S0BUF data and the RB80 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 D0

(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 n g D ia g ra m

RX D0

(D at a in )

Sa mp li ng R at e

UART0 Mode 1 Timing Diagram

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