PIC18F2331/2431/4331/4431
20.0
ENHANCED UNIVERSAL
SYNCHRONOUS
ASYNCHRONOUS RECEIVER
TRANSMITTER (EUSART)
The operation of the Enhanced USART module is
controlled through three registers:
• Transmit Status and Control (TXSTA)
• Receive Status and Control (RCSTA)
• Baud Rate Control (BAUDCON)
These are detailed on the following pages in
and
respectively.
The Enhanced Universal Synchronous Asynchronous
Receiver Transmitter (EUSART) module is one of the
two serial I/O modules available in the PIC18F2331/
2431/4331/4431 family of microcontrollers. EUSART is
also known as a Serial Communications Interface or
SCI.
The EUSART can be configured as a full-duplex
asynchronous system that can communicate with
peripheral devices, such as CRT terminals and
personal computers. It can also be configured as a half-
duplex synchronous system that can communicate
with peripheral devices, such as A/D or D/A integrated
circuits, serial EEPROMs, etc.
The EUSART module implements additional features,
including automatic baud rate detection and
calibration, automatic wake-up on Sync Break
reception and 12-bit Break character transmit. These
features make it ideally suited for use in Local
Interconnect Network (LIN/J2602) bus systems.
The EUSART can be configured in the following
modes:
• Asynchronous (full-duplex) with:
- Auto-wake-up on character reception
- Auto-baud calibration
- 12-bit Break character transmission
• Synchronous – Master (half-duplex) with
selectable clock polarity
• Synchronous – Slave (half-duplex) with selectable
clock polarity
In order to configure pins, TX and RX, as the Enhanced
Universal Synchronous Asynchronous Receiver
Transmitter:
• SPEN (RCSTA<7>) bit must be set ( =
1),
• TRISC<6> bit must be set ( =
1),
and
• TRISC<7> bit must be set ( =
1).
Note:
The EUSART control will automatically
reconfigure the pin from input to output as
needed.
20.1
Asynchronous Operation in
Power-Managed Modes
The EUSART may operate in Asynchronous mode
while the peripheral clocks are being provided by the
internal oscillator block. This makes it possible to
remove the crystal or resonator that is commonly con-
nected as the primary clock on the OSC1 and OSC2
pins.
The factory calibrates the internal oscillator block out-
put (INTOSC) for 8 MHz (see
However,
this frequency may drift as V
DD
or temperature
changes, and this directly affects the asynchronous
baud rate. Two methods may be used to adjust the
baud rate clock, but both require a reference clock
source of some kind.
The first (preferred) method uses the OSCTUNE
register to adjust the INTOSC output back to 8 MHz.
Adjusting the value in the OSCTUNE register allows for
fine resolution changes to the system clock source (see
for more
information).
The other method adjusts the value in the Baud Rate
Generator (BRG). There may not be fine enough
resolution when adjusting the Baud Rate Generator to
compensate for a gradual change in the peripheral
clock frequency.
2010 Microchip Technology Inc.
DS39616D-page 217
MICROCHIP [ MICROCHIP TECHNOLOGY ]
