em78f644nso28s ELAN Microelectronics Corp, em78f644nso28s Datasheet - Page 107

• Manufacturer Part Number: em78f644nso28s
• Description: Flash Series 8-bit Microcontroller
• Manufacturer: ELAN Microelectronics Corp

Product Specification (V1.0) 05.05.2010
(This specification is subject to change without further notice)
6.6 UART (Universal Asynchronous Receiver/Transmitter)
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. Double buffering for both sections allows the UART to be
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). 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.
Figure 6-12a UART Function Block Diagram
Figure 6-12b UART Data Format
EM78F648/644/642/641/548/544/542/541N
8-Bit Microcontroller
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