Datasheet

PIC18(L)F2X/45K50
DS30684A-page 260  2012 Microchip Technology Inc.
16.7 Baud Rate Generator
The MSSP module has a Baud Rate Generator avail-
able for clock generation in both I
2
C and SPI Master
modes. The Baud Rate Generator (BRG) reload value
is placed in the SSPxADD register (Register 16-6).
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 16-39 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 16-4 demonstrates clock rates based on
instruction cycles and the BRG value loaded into
SSPxADD.
EQUATION 16-1:
FIGURE 16-40: BAUD RATE GENERATOR BLOCK DIAGRAM
FCLOCK
FOSC
SSPxADD 1+4
-------------------------------------------------=
Note: Values of 0x00, 0x01 and 0x02 are not valid
for SSPxADD when used as a Baud Rate
Generator for I
2
C. This is an implementation
limitation.
SSPxM<3:0>
BRG Down Counter
SSPxCLK
F
OSC/2
SSPxADD<7:0>
SSPxM<3:0>
SCL
Reload
Control
Reload
TABLE 16-4: MSSP CLOCK RATE W/BRG
FOSC FCY BRG Value
F
CLOCK
(2 Rollovers of BRG)
32 MHz 8 MHz 13h 400 kHz
(1)
32 MHz 8 MHz 19h 308 kHz
32 MHz 8 MHz 4Fh 100 kHz
16 MHz 4 MHz 09h 400 kHz
(1)
16 MHz 4 MHz 0Ch 308 kHz
16 MHz 4 MHz 27h 100 kHz
4 MHz 1 MHz 09h 100 kHz
Note 1: The I
2
C interface does not conform to the 400 kHz I
2
C 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.