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Rev. 1.00
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Standard 8051 8-Bit Flash MCU
HT85F2260/HT85F2270/HT85F2280
UART Serial Interfaces – UART0 and UART1
UART Serial Interfaces – UART0 and UART1
UART1 Operating Description
This section provides a more detailed description of the UART1 structure and operation. The
following shows the overall UART1 block diagram.
UART1 Ba�d Rate
T�ansmit Shift Registe�
Cont�ol Unit
O�tp�t
Latch
RXD1
RI1
TI1
Receive Shift Registe�
Inp�t
Latch
S1BUF
TXD1
MCU Data B�s
UART1 Block Diagram
UART1 External Pin Interfacing
To communicate with an external serial interface, the internal UART1 each has two external
pins known as TXD1 and RXD1. The UART1 provides two operating modes both of which use
Asynchronous communication. The TXD1 pin is used to transmit data while the RXD1 pin is
used as the data reception pin. The TXD1 and RXD1 pins are pin shared with I/O pins. When the
UART1 function is disabled, controlled by the REN1 bit in the S1CON register, these two pins can
be used as general purpose I/O pins.