PIC18F2510 MICROCHIP [Microchip Technology], PIC18F2510 Datasheet - Page 197

• Manufacturer Part Number: PIC18F2510
• Description: 28/40/44-PIN FLASH MICROCONTROLLERS WITH 10-BIT A/D AND NANO WATT TECHNOLOGY
• Manufacturer: MICROCHIP [Microchip Technology]

17.1
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 17-1 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 17-1. From this,
the error in baud rate can be determined. An example
calculation is shown in Example 17-1. Typical baud
rates and error values for the various Asynchronous
modes
TABLE 17-1:
EXAMPLE 17-1:
TABLE 17-2:
 2004 Microchip Technology Inc.
Legend: x = Don’t care, n = value of SPBRGH:SPBRG register pair
TXSTA
RCSTA
BAUDCON ABDOVF
SPBRGH
SPBRG
Legend: — = unimplemented, read as ‘0’. Shaded cells are not used by the BRG.
For a device with F
Desired Baud Rate
Solving for SPBRGH:SPBRG:
Calculated Baud Rate
Error
Name
SYNC
0
0
0
0
1
1
are
Baud Rate Generator (BRG)
Configuration Bits
EUSART Baud Rate Generator Register, High Byte
EUSART Baud Rate Generator Register, Low Byte
shown
CSRC
SPEN
Bit 7
BAUD RATE FORMULAS
BRG16
REGISTERS ASSOCIATED WITH BAUD RATE GENERATOR
OSC
X
0
0
1
1
0
1
CALCULATING BAUD RATE ERROR
in
of 16 MHz, desired baud rate of 9600, Asynchronous mode, 8-bit BRG:
= F
= ((F
= ((16000000/9600)/64) – 1
= [25.042] = 25
= 16000000/(64 (25 + 1))
= 9615
= (Calculated Baud Rate – Desired Baud Rate)/Desired Baud Rate
= (9615 – 9600)/9600 = 0.16%
RCIDL
Bit 6
RX9
TX9
Table 17-2.
OSC
OSC
/(64 ([SPBRGH:SPBRG] + 1))
BRGH
/Desired Baud Rate)/64) – 1
0
1
0
1
x
x
OSC
SREN
TXEN
Bit 5
—
, the nearest
It
may
CREN
SYNC
SCKP
Bit 4
Preliminary
BRG/EUSART Mode
be
16-bit/Asynchronous
16-bit/Asynchronous
8-bit/Asynchronous
8-bit/Asynchronous
16-bit/Synchronous
8-bit/Synchronous
ADDEN
SENDB
BRG16
Bit 3
advantageous 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.
17.1.1
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.
17.1.2
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.
PIC18F2X1X/4X1X
BRGH
FERR
Bit 2
—
OPERATION IN POWER MANAGED
MODES
SAMPLING
OERR
TRMT
WUE
Bit 1
Baud Rate Formula
F
F
F
ABDEN
OSC
OSC
OSC
RX9D
TX9D
Bit 0
/[64 (n + 1)]
/[16 (n + 1)]
/[4 (n + 1)]
DS39636A-page 195
Reset Values
on page
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