PIC16C765 Microchip Technology Inc., PIC16C765 Datasheet - Page 79

• Manufacturer Part Number: PIC16C765
• Description: 8-bit Cmos Microcontrollers With Usb
• Manufacturer: Microchip Technology Inc.

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.
TABLE 11-1:
TABLE 11-2:
2000 Microchip Technology Inc.
Desired
SYNC
Baud
230400
460800
921600
115200
0
1
19200
38400
57600
1200
2400
4800
9600
300
USART Baud Rate Generator (BRG)
1000000.00
230769.23
461538.46
115384.62
Actual
38461.54
57692.31
Baud
BAUD RATE FORMULA
BAUD RATES FOR
SYNCHRONOUS MODE
(Asynchronous) Baud Rate = F
(Synchronous) Baud Rate = F
% of Error
24 MHz
BRGH = 0 (Low Speed)
INT
8.51
0.16
0.16
0.16
0.16
0.16
, the nearest inte-
SPBRG
INT
INT
155
103
Preliminary
51
25
12
5
/(64(SPBRG+1))
/(4(SPBRG+1))
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 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.
TABLE 11-3:
Desired
Baud
230400
460800
921600
115200
19200
38400
57600
1200
2400
4800
9600
300
SAMPLING
INT
PIC16C745/765
125000.00
Baud Rate = F
Actual
19736.84
41666.67
62500.00
Baud
/(16(X + 1)) equation can reduce the
2403.85
4807.69
9615.38
BAUD RATES FOR
ASYNCHRONOUS MODE
(BRGH = 0)
BRGH = 1 (High Speed)
% of Error
24 MHz
INT
NA
/(16(SPBRG+1))
0.16
0.16
0.16
2.80
8.51
8.51
8.51
DS41124C-page 79
SPBRG
155
77
38
18
8
5
2