PIC16C63A Microchip Technology, PIC16C63A Datasheet - Page 63

• Manufacturer Part Number: PIC16C63A
• Description: 28/40-Pin 8-Bit CMOS Microcontrollers
• Manufacturer: Microchip Technology

9.1
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 9-1 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 Fosc, the nearest inte-
ger value for the SPBRG register can be calculated
using the formula in Table 9-1. From this, the error in
baud rate can be determined.
Example 9-1 shows the calculation of the baud rate
error for the following conditions:
TABLE 9-1:
X = value in SPBRG (0 to 255)
TABLE 9-2:
Address
98h
18h
99h
Legend: x = unknown, - = unimplemented read as '0'. Shaded cells are not used by the BRG.
1998 Microchip Technology Inc.
SYNC
0
1
F
Desired Baud Rate = 9600
BRGH = 0
SYNC = 0
OSC
USART Baud Rate Generator (BRG)
Name
TXSTA
RCSTA
SPBRG
= 16 MHz
BAUD RATE FORMULA
REGISTERS ASSOCIATED WITH BAUD RATE GENERATOR
(Asynchronous) Baud Rate = F
(Synchronous) Baud Rate = F
CSRC
SPEN
Baud Rate Generator Register
Bit 7
BRGH = 0 (Low Speed)
TX9
RX9
Bit 6
TXEN SYNC —
SREN CREN —
Bit 5
Bit 4
OSC
OSC
PIC16C63A/65B/73B/74B
/(64(X+1))
/(4(X+1))
Bit 3
Desired Baud rate
Calculated Baud Rate =16000000 / (64 (25 + 1))
Error
EXAMPLE 9-1:
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.
9.1.1
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 TRMT TX9D
FERR
Bit 2
9600
X
=
=
=
=
SAMPLING
OERR RX9D
Bit 1
OSC
/(16(X + 1)) equation can reduce the
=Fosc / (64 (X + 1))
=16000000 /(64 (X + 1))
= 25.042 = 25
9615
(Calculated Baud Rate-Desired Baud Rate)
(9615 - 9600) / 9600
0.16%
Baud Rate= F
Bit 0
BRGH = 1 (High Speed)
CALCULATING BAUD
RATE ERROR
0000 -010
0000 -00x
0000 0000
Value on
Desired Baud Rate
POR,
BOR
NA
OSC
DS30605A-page 63
/(16(X+1))
0000 -010
0000 -00x
0000 0000
other resets
Value on all