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Rev. 1.21
132
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Rev. 1.21
133
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HT66F488/HT66F489
A/D Flash MCU with EEPROM
HT66F488/HT66F489
A/D Flash MCU with EEPROM
UART Data Transfer Scheme
The 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 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 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, 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.
MSB
LSB
…………………………
T�ans�itte� Shift Registe�
MSB
LSB
…………………………
Receive� Shift Registe�
TX Pin
RX Pin
Baud Rate
Gene�ato�
TXR Registe�
Buffe�
MCU Data Bus
RXR Registe�
CLK
CLK
UART Data Transfer Scheme
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.
Register
Name
Bit
7
6
5
4
3
2
1
0
USR
PERR
�F
FERR
OERR
RIDLE
RXIF
TIDLE
TXIF
UCR1
UARTE�
B�O
PRE�
PRT
STOPS
TXBRK
RX8
TX8
UCR2
TXE�
RXE�
BRGH
ADDE�
WAKE
RIE
TIIE
TEIE
TXR/RXR TXRX�
TXRX6
TXRX5
TXRX4
TXRX3
TXRX2
TXRX1
TXRX�
BRG
BRG�
BRG6
BRG5
BRG4
BRG3
BRG2
BRG1
BRG�
UART Register Summary