PIC18F2550-I/SP Microchip Technology Inc., PIC18F2550-I/SP Datasheet - Page 243

• Manufacturer Part Number: PIC18F2550-I/SP
• Description: Microcontroller; 32 KB Flash; 2048 RAM; 256 EEPROM; 24 I/O; 28-Pin-SPDIP
• Manufacturer: Microchip Technology Inc.

Specifications of PIC18F2550-I/SP

• A/d Inputs: 10-Channel, 10-Bit
• Comparators: 2
• Cpu Speed: 12 MIPS
• Eeprom Memory: 256 Bytes
• Input Output: 23
• Interface: I2C/SPI/USART/USB
• Memory Type: Flash
• Number Of Bits: 8
• Package Type: 28-pin SPDIP
• Programmable Memory: 32K Bytes
• Ram Size: 2K Bytes
• Speed: 48 MHz
• Timers: 1-8-bit, 3-16-bit
• Voltage, Range: 2-5.5 V
• Lead Free Status / Rohs Status: RoHS Compliant part Electrostatic Device

20.1
The BRG is a dedicated 8-bit, or 16-bit, generator that
supports both the Asynchronous and Synchronous
modes of the EUSART. By default, the BRG operates
in 8-bit mode. Setting the BRG16 bit (BAUDCON<3>)
selects 16-bit mode.
The SPBRGH:SPBRG register pair controls the period
of a free-running timer. In Asynchronous mode, bits
BRGH (TXSTA<2>) and BRG16 (BAUDCON<3>) also
control the baud rate. In Synchronous mode, BRGH is
ignored. Table 20-1 shows the formula for computation
of the baud rate for different EUSART modes which
only apply in Master mode (internally generated clock).
Given the desired baud rate and F
integer value for the SPBRGH:SPBRG registers can be
calculated using the formulas in Table 20-1. From this,
the error in baud rate can be determined. An example
calculation is shown in Example 20-1. Typical baud
rates and error values for the various Asynchronous
modes are shown in Table 20-2. It may be advantageous
TABLE 20-1:
© 2006 Microchip Technology Inc.
Legend: x = Don’t care, n = value of SPBRGH:SPBRG register pair
SYNC
0
0
0
0
1
1
Baud Rate Generator (BRG)
Configuration Bits
BAUD RATE FORMULAS
BRG16
0
0
1
1
0
1
BRGH
0
1
0
1
x
x
OSC
, the nearest
PIC18F2455/2550/4455/4550
Preliminary
BRG/EUSART Mode
16-bit/Asynchronous
16-bit/Asynchronous
8-bit/Asynchronous
8-bit/Asynchronous
16-bit/Synchronous
8-bit/Synchronous
to use the high baud rate (BRGH = 1), or the 16-bit BRG
to reduce the baud rate error, or achieve a slow baud
rate for a fast oscillator frequency.
Writing a new value to the SPBRGH:SPBRG registers
causes the BRG timer to be reset (or cleared). This
ensures the BRG does not wait for a timer overflow
before outputting the new baud rate.
20.1.1
The device clock is used to generate the desired baud
rate. When one of the power-managed modes is
entered, the new clock source may be operating at a
different frequency. This may require an adjustment to
the value in the SPBRG register pair.
20.1.2
The data on the RX pin is sampled three times by a
majority detect circuit to determine if a high or a low
level is present at the RX pin.
OPERATION IN POWER-MANAGED
MODES
SAMPLING
Baud Rate Formula
F
F
F
OSC
OSC
OSC
/[64 (n + 1)]
/[16 (n + 1)]
/[4 (n + 1)]
DS39632C-page 241