PIC16F747 Microchip Technology Inc., PIC16F747 Datasheet - Page 137

• Manufacturer Part Number: PIC16F747
• Description: 28/40/44-pin, 8-bit Cmos Flash Microcontrollers With 10-bit A/d And Nanowatt Technology
• Manufacturer: Microchip Technology Inc.

11.1
The BRG supports both the Asynchronous and
Synchronous modes of the AUSART. It is a dedicated
8-bit Baud Rate Generator. The SPBRG register
controls the period of a free running 8-bit timer. In
Asynchronous mode, bit BRGH (TXSTA<2>) also
controls the baud rate. In Synchronous mode, bit
BRGH is ignored. Table 11-1 shows the formula for
computation of the baud rate for different AUSART
modes which only apply in Master mode (internal
clock).
Given the desired baud rate and F
integer value for the SPBRG register can be calculated
using the formula in Table 11-1. From this, the error in
baud rate can be determined.
TABLE 11-1:
TABLE 11-2:
 2004 Microchip Technology Inc.
Legend: X = value in SPBRG (0 to 255).
98h
18h
99h
Legend:
Address
SYNC
0
1
AUSART Baud Rate Generator
(BRG)
TXSTA
RCSTA
SPBRG
x = unknown, — = unimplemented, read as ‘0’. Shaded cells are not used by the BRG.
Name
(Asynchronous) Baud Rate = F
(Synchronous) Baud Rate = F
BAUD RATE FORMULA
REGISTERS ASSOCIATED WITH BAUD RATE GENERATOR
Baud Rate Generator Register
CSRC
SPEN
Bit 7
BRGH = 0 (Low Speed)
Bit 6
RX9
TX9
OSC
SREN
TXEN
Bit 5
, the nearest
OSC
OSC
CREN
SYNC
Bit 4
/(64(X + 1))
/(4(X + 1))
ADDEN
Bit 3
—
It may be advantageous to use the high baud rate
(BRGH = 1) even for slower baud clocks. This is
because the F
baud rate error in some cases.
Writing a new value to the SPBRG register 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.
11.1.1
The data on the RC7/RX/DT 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.
BRGH
FERR
Bit 2
SAMPLING
OERR
TRMT
Bit 1
Baud Rate = F
OSC
BRGH = 1 (High Speed)
/(16(X + 1)) equation can reduce the
RX9D
TX9D
Bit 0
PIC16F7X7
N/A
OSC
0000 -010
0000 000x
0000 0000
POR, BOR
Value on:
/(16(X + 1))
DS30498C-page 135
0000 -010
0000 000x
0000 0000
Value on
all other
Resets