PIC16F87XA datasheet(99/234 Pages) MICROCHIP

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 2003 Microchip Technology Inc.

DS39582B-page 97

PIC16F87XA

9.4.7

BAUD RATE GENERATOR

In I2C Master mode, the Baud Rate Generator (BRG)

reload value is placed in the lower 7 bits of the

SSPADD register (Figure 9-17). When a write occurs to

SSPBUF, the Baud Rate Generator will automatically

begin counting. The BRG counts down to 0 and stops

until another reload has taken place. The BRG count is

decremented twice per instruction cycle (TCY) on the

Q2 and Q4 clocks. In I2C Master mode, the BRG is

reloaded automatically.

Once the given operation is complete (i.e., transmis-

sion of the last data bit is followed by ACK), the internal

clock will automatically stop counting and the SCL pin

will remain in its last state.

Table 9-3

demonstrates

clock

rates

based

instruction cycles and the BRG value loaded into

SSPADD.

FIGURE 9-17:

BAUD RATE GENERATOR BLOCK DIAGRAM

TABLE 9-3:

I2C CLOCK RATE W/BRG

SSPM3:SSPM0

BRG Down Counter

CLKO

FOSC/4

SSPADD<6:0>

SSPM3:SSPM0

SCL

Reload

Control

Reload

FCY

FCY*2

BRG Value

FSCL

(2 Rollovers of BRG)

10 MHz

20 MHz

19h

400 kHz(1)

10 MHz

20 MHz

20h

312.5 kHz

10 MHz

20 MHz

3Fh

100 kHz

4 MHz

8 MHz

0Ah

400 kHz(1)

4 MHz

8 MHz

0Dh

308 kHz

4 MHz

8 MHz

28h

100 kHz

1 MHz

2 MHz

03h

333 kHz(1)

1 MHz

2 MHz

0Ah

100 kHz

1 MHz

2 MHz

00h

1 MHz(1)

Note 1:

The I2C interface does not conform to the 400 kHz I2C specification (which applies to rates greater than

100 kHz) in all details, but may be used with care where higher rates are required by the application.

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