Datasheet

PIC16(L)F1512/3
DS41624B-page 230 Preliminary  2012 Microchip Technology Inc.
20.7 BAUD RATE GENERATOR
The MSSP module has a Baud Rate Generator
available for clock generation in both I
2
C and SPI
Master modes. The Baud Rate Generator (BRG)
reload value is placed in the SSPADD register
(Register 20-6). When a write occurs to SSPBUF, the
Baud Rate Generator 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 20-39 triggers the
value from SSPADD 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 20-4 demonstrates clock rates based on
instruction cycles and the BRG value loaded into
SSPADD.
EQUATION 20-1:
FIGURE 20-40: BAUD RATE GENERATOR BLOCK DIAGRAM
TABLE 20-4: MSSP CLOCK RATE W/BRG
FCLOCK
FOSC
SSPADD 1+4
----------------------------------------------=
Note: Values of 0x00, 0x01 and 0x02 are not valid
for SSPADD when used as a Baud Rate
Generator for I
2
C. This is an implementation
limitation.
FOSC FCY BRG Value
F
CLOCK
(2 Rollovers of BRG)
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.
SSPM<3:0>
BRG Down Counter
SSPCLK
F
OSC/2
SSPADD<7:0>
SSPM<3:0>
SCL
Reload
Control
Reload