EM78P311SXSSLASHXJ datasheet(33/68 Pages) EMC

33 / 68 page

EM78P311N

8-Bit Microcontroller

Product Specification (V1.0) 10.02.2006

• 29

(This specification is subject to change without further notice)

The figure below shows the general format of one character sent or received. The

communication channel is normally held in the marked state (high). Character

transmission or reception starts with a transition to the space state (low).

The first bit transmitted or received is the start bit (low). It is followed by the data bits, in

which the least significant bit (LSB) comes first. The data bits are followed by the parity

bit. If present, then the stop bit or bits (high) confirm the end of the frame.

In receiving, the UART synchronizes on the falling edge of the start bit. When two or

three “0” are detected during three samples, it is recognized as normal start bit and the

receiving operation is started.

START

bit

Parity

bit

STOP

bit

1 bit

7 or 8 bits

One character or frame

1 bit

1 bits

Idle state

(mark)

Fig. 5-11 Data Format in UART

5.7.1 UART Mode

There are three UART modes. Mode 1 (7 bits data) and Mode 2 (8 bits data) allow the

addition of a parity bit. The parity bit addition is not available in Mode 3. The Figure

below shows the data format in each mode.

UMODE

PRE

123

START

STOP

7 bits DATA

START

STOP

7 bits DATA

Parity

START

STOP

8 bits DATA

START

STOP

8 bits DATA

Parity

START

STOP

9 bits DATA

Mode 1

Mode 3

Mode 2

Fig. 5-12 UART Mode

5.7.2 Transmitting

In transmitting serial data, the UART operates as follows:

1. Set the TXE bit of the URC1 register to enable the UART transmission function.

2. Write data into the URTD register and the UTBE bit of the URC1 register will be set

by hardware.

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