BS66F340 Datasheet, PDF (185/256 Pages) Holtek Semiconductor Inc – Enhanced Touch A/D Flash MCU with LED Driver

BS66F340/BS66F350/BS66F360/BS66F370
Enhanced Touch A/D Flash MCU with LED Driver
T�ans�itte� Shift Registe� (TSR)
MSB ………………………… LSB
TX Pin RX Pin
Re�eive� Shift Registe� (RSR)
MSB ………………………… LSB
TX Registe� (TXR)
f_SYS
Data to �e t�ans�itted
Baud Rate
Gene�ato�
RX Registe� (RXR)
Buffe�
Data �e�eived
MCU Data Bus
UART Data Transfer Block Diagram
UART External Pin
To communicate with an external serial interface, the internal UART has two external pins known
as TX and RX. The TX and RX pins are the UART transmitter and receiver pins respectively. The
TX and RX pin function should first be selected by the corresponding pin-shared function selection
register before the UART function is used. Along with the UARTEN bit, the TXEN and RXEN bits,
if set, will automatically setup these I/O or other pin-shared functional pins to their respective TX
output and RX input conditions and disable any pull-high resistor option which may exist on the
TX and RX pins. When the TX or RX pin function is disabled by clearing the UARTEN, TXEN or
RXEN bit, the TX or RX pin will be set to a floating state. At this time whether the internal pull-
high resistor is connected to the TX or RX pin or not is determined by the corresponding I/O pull-
high function control bit.
UART Data Transfer Scheme
The above diagram shows the overall data transfer structure arrangement for the UART interface.
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 Transmit Shift Register 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 mapped onto the MCU Data Memory, the Transmit Shift Register is not mapped
and is therefore inaccessible to the application program.
Data to be received by the UART is accepted on the external RX pin, from where it is shifted in,
LSB first, to the Receiver Shift Register 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 TXR
register is mapped onto the MCU Data Memory, the Receiver Shift Register is not mapped and is
therefore inaccessible to the application program.
It should be noted that the actual register for data transmission 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 in the Data Memory. This shared register known as the TXR_RXR register is used
for both data transmission and data reception.
UART Status and Control Registers
There are five control registers associated with the UART function. The USR, UCR1 and UCR2
registers control the overall function of the UART, while the BRG register controls the Baud rate.
The actual data to be transmitted and received on the serial interface is managed through the TXR_
RXR data registers.
Rev. 1.40
185
December 15, 2016