EM78P809N
8-Bit Microcontroller
Product Specification (V1.0) 07.26 .2 005 • 35
(This specification is subject to change without further notice)
4.7.2 Transmitting: In transmitting serial data, the UART operates as follows:
1. Set the TXE bit of the URC1 register to enable the UAR T transmission function.
2. Write data into the URTD register and th e UTBE bit of the URC1 register will be set
by hardware.
3. The n start transmitting.
4. Ser ially transmitted data are transmitted in th e following order from the TX pin.
5. Start bit: one “0” bit is output.
6. Transmit data: 7, 8 or 9 bits data are output from the LSB to the MSB.
7. Parity bit: one parity bit (odd or even selectable) is output.
8. St op bit: one “1” bit (stop bit) is output.
Mark state: output “1” continues un til the start bit of the next transmitted data .
After transmitting the stop bit, the UART generates a TBEF interrupt (if enabled).
4.7.3 Receiving: In receiving, the UART operates as follows:
1. Set RXE bit of the URS register to enable the UART receiving function.
The UART monitors the RX pin and synchronizes internally when it detects a start
bit.
2. Receive data is shifted into the URRD reg ister in the order from LSB to MSB.
3. The parity bit and the stop bit are received.
After one character received, the UART ge nerates a RBFF interrupt (if enable).
And URBF bit of URS register will be set to 1.
4. The UART makes the following checks:
(a) Parity check: The number of 1 of the received data must match the even or
odd parity setting of the EVEN bit in the URS register.
(b) Frame check: The start bit must be 0 and the stop bit must be 1.
(c) Overrun check: The URBF bit of the URS register must be cleared (that
means the URRD register should be read out) before next received data is load ed
into the URRD register.
If any checks failed, the UERR IF interrupt will be generated (if enabled) , and an
error flag is indicated in PRERR, OVERR or FMERR bit. The error flag should be
cleared by software else the UERRIF interrupt will occur when the next byte is
received.
5. Read received data from URRD register. And URBF bit will be clear by hardware.