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Rev. 1.00
138
October 26, 2018
Rev. 1.00
139
October 26, 2018
BS86DH12C
High Voltage Touch A/D Flash MCU with HVIO
BS86DH12C
High Voltage Touch A/D Flash MCU with HVIO
UART External Pins
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 configure these 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 placed
into 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 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_RXR 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_RXR 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 TXR_RXR
register, where it is buffered and can be manipulated by the application program. Only the TXR_RXR
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 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 register.
Register
Name
Bit
7
6
5
4
3
2
1
0
USR
PERR
NF
FERR
OERR
RIDLE
RXIF
TIDLE
TXIF
UCR1
UARTEN
BNO
PREN
PRT
STOPS
TXBRK
RX8
TX8
UCR2
TXEN
RXEN
BRGH
ADDEN
WAKE
RIE
TIIE
TEIE
TXR_RXR
D7
D6
D5
D4
D3
D2
D1
D0
BRG
D7
D6
D5
D4
D3
D2
D1
D0
UART Register List