em78p809n ELAN Microelectronics Corp, em78p809n Datasheet - Page 38

• Manufacturer Part Number: em78p809n
• Description: 8-bit Microcontroller
• Manufacturer: ELAN Microelectronics Corp

EM78P809N
8-Bit Microcontroller
34 •
4.7.1 UART MODE:
In Universal Asynchronous Receiver Transmitter (UART), each transmitted or received
character is individually synchronized by framing it with a start bit and stop bit.
Full duplex data transfer is possible since the UART has independent transmit and
receive sections.
programmed for continuous data transfer.
The figure below shows the general format of one character sent or received. The
communication channel is normally held in the marked state (high).
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.
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.
Mode 1
Mode 2
Mode 3
START
1 bit
bit
UMODE
0
0
0
0
1
D0
0
0
1
1
0
Fig. 12. DATA Format in UART
Double buffering for both sections allows the UART to be
D1
PRE
0
1
0
1
X
D2
7 or 8 bits
One character or frame
Fig. 13. UART Mode
START
START
START
START
START
1
(This specification is subject to change without further notice)
2
3
Product Specification (V1.0) 07.26.2005
4
7 bits DATA
7 bits DATA
8 bits DATA
8 bits DATA
9 bits DATA
5
Dn
6
Parity
1 bit
7
bit
8
STOP
STOP
Parity
bit
9
1 bits
STOP
Parity
10
STOP
STOP
STOP
Character
Idle state
(mark)
11