Datasheet

© 2007 Microchip Technology Inc. DS39605F-page 143
PIC18F1220/1320
16.3.2 EUSART ASYNCHRONOUS
RECEIVER
The receiver block diagram is shown in Figure 16-5.
The data is received on the RB4/AN6/RX/DT/KBI0 pin
and drives the data recovery block. The data recovery
block is actually a high-speed shifter, operating at x16
times the baud rate, whereas the main receive serial
shifter operates at the bit rate or at F
OSC. This mode
would typically be used in RS-232 systems.
To set up an Asynchronous Reception:
1. Initialize the SPBRGH:SPBRG registers for the
appropriate baud rate. Set or clear the BRGH
and BRG16 bits, as required, to achieve the
desired baud rate.
2. Enable the asynchronous serial port by clearing
bit SYNC and setting bit SPEN.
3. If interrupts are desired, set enable bit RCIE.
4. If 9-bit reception is desired, set bit RX9.
5. Enable the reception by setting bit CREN.
6. Flag bit, RCIF, will be set when reception is
complete and an interrupt will be generated if
enable bit RCIE was set.
7. Read the RCSTA register to get the 9th bit (if
enabled) and determine if any error occurred
during reception.
8. Read the 8-bit received data by reading the
RCREG register.
9. If any error occurred, clear the error by clearing
enable bit CREN.
10. If using interrupts, ensure that the GIE and PEIE
bits in the INTCON register (INTCON<7:6>) are
set.
16.3.3 SETTING UP 9-BIT MODE WITH
ADDRESS DETECT
This mode would typically be used in RS-485 systems.
To set up an Asynchronous Reception with Address
Detect Enable:
1. Initialize the SPBRGH:SPBRG registers for the
appropriate baud rate. Set or clear the BRGH
and BRG16 bits, as required, to achieve the
desired baud rate.
2. Enable the asynchronous serial port by clearing
the SYNC bit and setting the SPEN bit.
3. If interrupts are required, set the RCEN bit and
select the desired priority level with the RCIP bit.
4. Set the RX9 bit to enable 9-bit reception.
5. Set the ADDEN bit to enable address detect.
6. Enable reception by setting the CREN bit.
7. The RCIF bit will be set when reception is
complete. The interrupt will be Acknowledged if
the RCIE and GIE bits are set.
8. Read the RCSTA register to determine if any
error occurred during reception, as well as read
bit 9 of data (if applicable).
9. Read RCREG to determine if the device is being
addressed.
10. If any error occurred, clear the CREN bit.
11. If the device has been addressed, clear the
ADDEN bit to allow all received data into the
receive buffer and interrupt the CPU.
FIGURE 16-5: EUSART RECEIVE BLOCK DIAGRAM
x64 Baud Rate CLK
Baud Rate Generator
RB4/AN6/RX/DT/KBI0
Pin Buffer
and Control
SPEN
Data
Recovery
CREN
OERR FERR
RSR Register
MSb
LSb
RX9D
RCREG Register
FIFO
Interrupt
RCIF
RCIE
Data Bus
8
÷ 64
÷ 16
or
Stop
Start
(8) 7 1 0
RX9
• • •
SPBRGSPBRGH
BRG16
or
÷ 4