PIC16C745/P Microchip Technology, PIC16C745/P Datasheet - Page 77

• Manufacturer Part Number: PIC16C745/P
• Description: 8-Bit CMOS Microcontrollers with USB
• Manufacturer: Microchip Technology

11.1
The BRG supports both the asynchronous and syn-
chronous modes of the USART. 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 USART modes which only apply
in master mode (internal clock).
Given the desired baud rate and F
ger 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.
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.
TABLE 11-1:
TABLE 11-2:
1999 Microchip Technology Inc.
Desired
SYNC
Baud
0
1
115200 125000.00
230400 250000.00
460800 500000.00
921600
19200
38400
57600
1200
2400
4800
9600
USART Baud Rate Generator (BRG)
300
INT
Actual
19230.77
38461.54
58823.53
Baud
4807.69
9615.38
/(16(X + 1)) equation can reduce the
BAUD RATE FORMULA
BAUD RATES FOR SYNCHRONOUS MODE
(Asynchronous) Baud Rate = F
(Synchronous) Baud Rate = F
4 MHz
Error
% of
BRGH = 0 (Low Speed)
0.16
0.16
0.16
0.16
2.12
8.51
8.51
8.51
INT
, the nearest inte-
SPBRG
Advanced Information
207
103
51
25
16
7 115384.62
3 250000.00
1 500000.00
INT
INT
Actual
19230.77
38461.54
57692.31
Baud
9615.38
/(64(SPBRG+1))
/(4(SPBRG+1))
6 MHz
Error
% of
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 output-
ting the new baud rate.
11.1.1
The data on the RC7/RX/DT pin is sampled three times
near the center of each bit time by a majority detect cir-
cuit to determine if a high or a low level is present at the
RX pin.
0.16
0.16
0.16
0.16
0.16
8.51
8.51
SAMPLING
SPBRG
PIC16C745/765
155
Baud Rate= F
77
38
25
12
5
2
1000000.00
BRGH = 1 (High Speed)
115384.62
230769.23
461538.46
Actual
Baud
38461.54
57692.31
INT
NA
24 MHz
/(16(SPBRG+1))
Error
% of
DS41124A-page 77
0.16
0.16
0.16
0.16
0.16
8.51
SPBRG
155
103
51
25
12
5