PIC18F44J10 datasheet(180/368 Pages) MICROCHIP

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PIC18F45J10 FAMILY

DS39682E-page 178

16.4.7

BAUD RATE

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

reload value is placed in the lower 7 bits of the

SSPxADD register (Figure 16-17). When a write

occurs to SSPxBUF, 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 SCLx pin

will remain in its last state.

Table 16-3 demonstrates clock rates based on

instruction cycles and the BRG value loaded into

SSPxADD.

16.4.7.1

Baud Rate and Module

Interdependence

Because MSSP1 and MSSP2 are independent, they

can operate simultaneously in I2C Master mode at

different baud rates. This is done by using different

BRG reload values for each module.

Because this mode derives its basic clock source from

the system clock, any changes to the clock will affect

both modules in the same proportion. It may be pos-

sible to change one or both baud rates back to a

previous value by changing the BRG reload value.

FIGURE 16-17:

BAUD RATE GENERATOR BLOCK DIAGRAM

TABLE 16-3:

I2C™ CLOCK RATE w/BRG

SSPM<3:0>

BRG Down Counter

CLKO

FOSC/4

SSPxADD<6:0>

SSPM<3:0>

SCLx

Reload

Control

Reload

FCY

FCY * 2

BRG Value

FSCL

(2 Rollovers of BRG)

10 MHz

20 MHz

18h

400 kHz(1)

10 MHz

20 MHz

1Fh

312.5 kHz

10 MHz

20 MHz

63h

100 kHz

4 MHz

8 MHz

09h

400 kHz(1)

4 MHz

8 MHz

0Ch

308 kHz

4 MHz

8 MHz

27h

100 kHz

1 MHz

2 MHz

02h

333 kHz(1)

1 MHz

2 MHz

09h

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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