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Rev. 1.00
146
October 26, 2018
Rev. 1.00
147
October 26, 2018
BS86DH12C
High Voltage Touch A/D Flash MCU with HVIO
BS86DH12C
High Voltage Touch A/D Flash MCU with HVIO
TXEN bit is set, but the data will not be transmitted until the TXR_RXR register has been loaded
with data and the baud rate generator has defined a shift clock source. However, the transmission
can also be initiated by first loading data into the TXR_RXR register, after which the TXEN bit can
be set. When a transmission of data begins, the TSR is normally empty, in which case a transfer to
the TXR_RXR register will result in an immediate transfer to the TSR. If during a transmission the
TXEN bit is cleared, the transmission will immediately cease and the transmitter will be reset. The
TX output pin can then be in a floating state.
Transmitting Data
When the UART is transmitting data, the data is shifted on the TX pin from the shift register, with
the least significant bit first. In the transmit mode, the TXR_RXR register forms a buffer between
the internal bus and the transmitter shift register. It should be noted that if 9-bit data format has been
selected, then the MSB will be taken from the TX8 bit in the UCR1 register. The steps to initiate a
data transfer can be summarized as follows:
• Make the correct selection of the BNO, PRT, PREN and STOPS bits to define the required word
length, parity type and number of stop bits.
• Configure the BRG register to select the desired baud rate.
• Set the TXEN bit to ensure that the TX pin is used as a UART transmitter pin.
• Access the USR register and write the data that is to be transmitted into the TXR_RXR register.
Note that this step will clear the TXIF bit.
This sequence of events can now be repeated to send additional data.
It should be noted that when TXIF=0, data will be inhibited from being written to the TXR_RXR
register. Clearing the TXIF flag is always achieved using the following software sequence:
1. A USR register access
2. A TXR_RXR register write execution
The read-only TXIF flag is set by the UART hardware and if set indicates that the TXR_RXR
register is empty and that other data can now be written into the TXR_RXR register without
overwriting the previous data. If the TEIE bit is set then the TXIF flag will generate an interrupt.
During a data transmission, a write instruction to the TXR_RXR register will place the data into the
TXR_RXR register, which will be copied to the shift register at the end of the present transmission.
When there is no data transmission in progress, a write instruction to the TXR_RXR register will
place the data directly into the shift register, resulting in the commencement of data transmission,
and the TXIF bit being immediately set. When a frame transmission is complete, which happens
after stop bits are sent or after the break frame, the TIDLE bit will be set. To clear the TIDLE bit the
following software sequence is used:
1. A USR register access
2. A TXR_RXR register write execution
Note that both the TXIF and TIDLE bits are cleared by the same software sequence.
Transmit Break
If the TXBRK bit is set then break characters will be sent on the next transmission. Break character
transmission consists of a start bit, followed by 13×N ‘0’ bits and stop bits, where N=1, 2, etc. If a
break character is to be transmitted then the TXBRK bit must be first set by the application program,
and then cleared to generate the stop bits. Transmitting a break character will not generate a transmit
interrupt. Note that a break condition length is at least 13 bits long. If the TXBRK bit is continually
kept at a logic high level then the transmitter circuitry will transmit continuous break characters.
After the application program has cleared the TXBRK bit, the transmitter will finish transmitting the