PIC16 datasheet(229/418 Pages) MICROCHIP

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 2011-2013 Microchip Technology Inc.

DS40001609C-page 229

PIC16(L)F1508/9

21.7

BAUD RATE GENERATOR

The MSSP module has a Baud Rate Generator avail-

able for clock generation in both I2C and SPI Master

modes. The Baud Rate Generator (BRG) reload value

is placed in the SSPxADD register (Register 21-6).

When a write occurs to SSPxBUF, the Baud Rate Gen-

erator will automatically begin counting down.

Once the given operation is complete, the internal clock

will automatically stop counting and the clock pin will

remain in its last state.

An internal signal “Reload” in Figure 21-40 triggers the

value from SSPxADD to be loaded into the BRG

counter. This occurs twice for each oscillation of the

module clock line. The logic dictating when the reload

signal is asserted depends on the mode the MSSP is

being operated in.

Table 21-4 demonstrates clock rates based on

instruction cycles and the BRG value loaded into

SSPxADD.

EQUATION 21-1:

FIGURE 21-40:

BAUD RATE GENERATOR BLOCK DIAGRAM

TABLE 21-4:

MSSP CLOCK RATE W/BRG

FCLOCK

FOSC

SSPxADD

 4



-------------------------------------------------

Note: Values of 0x00, 0x01 and 0x02 are not valid

for SSPxADD when used as a Baud Rate

Generator for I2C. This is an implementation

limitation.

FOSC

FCY

BRG Value

FCLOCK

(Two Rollovers of BRG)

16 MHz

4 MHz

09h

400 kHz

16 MHz

4 MHz

0Ch

308 kHz

16 MHz

4 MHz

27h

100 kHz

4 MHz

1 MHz

09h

100 kHz

Note:

Refer to the I/O port electrical specifications in Table 29-4 to ensure the system is designed to support lol

requirements.

SSPM <3:0>

SSPxADD<7:0>

SSPxCLK

BRG Down Counter

FOSC/2

SSPM <3:0>

SCLx

Reload

Control

Reload

Rev. 10-000112A

7/30/2013

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