PIC18F452-I/L Microchip Technology Inc., PIC18F452-I/L Datasheet - Page 174

• Manufacturer Part Number: PIC18F452-I/L
• Description: 44 PIN, 32 KB FLASH, 1536 RAM, 34 I/O
• Manufacturer: Microchip Technology Inc.

Specifications of PIC18F452-I/L

• A/d Inputs: 8-Channel, 10-Bit
• Comparators: 2
• Cpu Speed: 10 MIPS
• Eeprom Memory: 256 Bytes
• Input Output: 36
• Interface: I2C/SPI/USART
• Memory Type: Flash
• Number Of Bits: 8
• Package Type: 44-pin PLCC
• Programmable Memory: 32K Bytes
• Ram Size: 1.5K Bytes
• Speed: 40 MHz
• Timers: 1-8-bit, 3-16-bit
• Voltage, Range: 2-5.5 V
• Lead Free Status / Rohs Status: RoHS Compliant part Electrostatic Device

PIC18FXX2
16.2
In this mode, the USART uses standard non-return-to-
zero (NRZ) format (one START bit, eight or nine data
bits and one STOP bit). The most common data format
is 8-bits. An on-chip dedicated 8-bit baud rate genera-
tor can be used to derive standard baud rate frequen-
cies from the oscillator. The USART transmits and
receives the LSb first. The USART’s transmitter and
receiver are functionally independent, but use the
same data format and baud rate. The baud rate gener-
ator produces a clock, either x16 or x64 of the bit shift
rate, depending on bit BRGH (TXSTA<2>). Parity is not
supported by the hardware, but can be implemented in
software (and stored as the ninth data bit).
Asynchronous mode is stopped during SLEEP.
Asynchronous mode is selected by clearing bit SYNC
(TXSTA<4>).
The USART Asynchronous module consists of the
following important elements:
• Baud Rate Generator
• Sampling Circuit
• Asynchronous Transmitter
• Asynchronous Receiver
16.2.1
The USART transmitter block diagram is shown in
Figure 16-1. The heart of the transmitter is the Transmit
(serial) Shift Register (TSR). The shift register obtains
its data from the read/write transmit buffer, TXREG. The
TXREG register is loaded with data in software. The
TSR register is not loaded until the STOP bit has been
transmitted from the previous load. As soon as the
STOP bit is transmitted, the TSR is loaded with new
data from the TXREG register (if available). Once the
TXREG register transfers the data to the TSR register
(occurs in one T
FIGURE 16-1:
DS39564C-page 172
USART Asynchronous Mode
USART ASYNCHRONOUS
TRANSMITTER
TXIE
CY
Interrupt
), the TXREG register is empty and
USART TRANSMIT BLOCK DIAGRAM
TXIF
TXEN
Baud Rate Generator
SPBRG
Baud Rate CLK
MSb
(8)
TX9D
TSR Register
TX9
TXREG Register
8
Data Bus
flag bit TXIF (PIR1<4>) is set. This interrupt can be
enabled/disabled by setting/clearing enable bit TXIE
( PIE1<4>). Flag bit TXIF will be set, regardless of the
state of enable bit TXIE and cannot be cleared in soft-
ware. It will reset only when new data is loaded into the
TXREG register. While flag bit TXIF indicated the sta-
tus of the TXREG register, another bit, TRMT
(TXSTA<1>), shows the status of the TSR register. Sta-
tus bit TRMT is a read-only bit, which is set when the
TSR register is empty. No interrupt logic is tied to this
bit, so the user has to poll this bit in order to determine
if the TSR register is empty.
To set up an asynchronous transmission:
1.
2.
3.
4.
5.
6.
7.
Note:
Note 1: The TSR register is not mapped in data
Initialize the SPBRG register for the appropriate
baud rate. If a high speed baud rate is desired,
set bit BRGH (Section 16.1).
Enable the asynchronous serial port by clearing
bit SYNC and setting bit SPEN.
If interrupts are desired, set enable bit TXIE.
If 9-bit transmission is desired, set transmit bit
TX9. Can be used as address/data bit.
Enable the transmission by setting bit TXEN,
which will also set bit TXIF.
If 9-bit transmission is selected, the ninth bit
should be loaded in bit TX9D.
Load data to the TXREG register (starts
transmission).
LSb
0
2: Flag bit TXIF is set when enable bit TXEN
TXIF is not cleared immediately upon load-
ing data into the transmit buffer TXREG.
The flag bit becomes valid in the second
instruction
instruction.
memory, so it is not available to the user.
is set.
TRMT
Pin Buffer
and Control
© 2006 Microchip Technology Inc.
cycle
SPEN
following
RC6/TX/CK pin
the
load