HT45B0F datasheet(6/23 Pages) HOLTEK

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HT45B0F

Rev. 1.00

June 7, 2011

Pin Interfacing

The UART has two pins known as TX and RX. The TX

pin is the UART transmitter serial data output pin if the

corresponding control bits named UARTEN in UCR1

control bit UARTEN or TXEN is equal to zero, the TX pin

is in the state of high impedance. Similarly, the RX pin is

the UART receiver serial data input pin if the corre-

sponding control bits named UARTEN and RXEN in

UCR1 and UCR2 registers are set to 1. If the control bit

UARTEN or RXEN is equal to zero, the RX pin is in the

state of high impedance.

UART Data Transfer Scheme

The following block diagram shows the overall data

transfer structure arrangement for the UART. The actual

data to be transmitted from the MCU is first transferred

to the TXR register by the application program. The data

will then be transferred to the Transmitter Shift Register

named TSR from where it will be shifted out, LSB first,

onto the TX pin at a rate controlled by the Baud Rate

Generator. Only the TXR register is accessible to the

application program, the Transmitter Shift Register is

not mapped into the Data Memory area and is inacces-

sible to the application program.

Data to be received by the UART is accepted on the RX

pin, from where it is shifted in, LSB first, to the Receiver

Shift Register named RSR at a rate controlled by the

Baud Rate Generator. When the shift register is full, the

data will then be transferred from the shift register to the

internal RXR register, where it is buffered and can be

manipulated by the application program. Only the RXR

ceiver Shift Register is not mapped into the Data Mem-

ory area and is inaccessible to the application program.

It should be noted that the actual register for data trans-

mission and reception, although referred to in the text,

and in application programs, as separate TXR and RXR

registers, only exists as a single shared register physi-

cally. This shared register known as the TXR/RXR regis-

ter is used for both data transmission and data

reception.

SDO

SDI

SCK

SCS

Writing Type Format: 8-bit Command Input + 8-bit Data Input

SDO

SDI

SCK

SCS

Reading Type Format: 8-bit Command Input + 8-bit Data Output

MSB

LSB

Transmitter Shift Register (TSR)

MSB

LSB

Receiver Shift Register (RSR)

TX Pin

RX Pin

Baud Rate

Generator

TX Register (TXR)

RX Register (RXR)

Buffer 1

Buffer 2

Buffer 3

Data to be transmitted

Data received

UART Data Transfer Scheme

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