HT85F2270 datasheet(207/226 Pages) HOLTEK

207 / 226 page

Rev. 1.00

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Standard 8051 8-Bit Flash MCU

HT85F2260/HT85F2270/HT85F2280

Mode 2

Mode 2 is an integrated full-duplex asynchronous serial communication interface. The 9 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

is fixed at a value of SP0CLK/32 or SP0CLK/64, depending on the setting of 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 9 bits of data where the 9th bit is taken

from the TB80 bit of the S0CON register, after which a stop bit, always “1”, is transmitted.

Data to be received by the UART0 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 9th bit is available as the RB80 bit

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 ng D ia gr am

RX D0

(D at a in )

Sa mp li ng R at e

TB 80

RB 80

UART0 Mode 2 Timing Diagram

HT85F2270 Datasheet(PDF) 207 Page - Holtek Semiconductor Inc

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