PIC18F23K22 Datasheet, PDF (254/492 Pages) Microchip Technology – 28/40/44-Pin, Low-Power, High-Performance Microcontrollers with nanoWatt XLP Technology

PIC18(L)F2X/4XK22
15.7 BAUD RATE GENERATOR
The MSSPx 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 15-6).
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 15-39 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 MSSPx is
being operated in.
Table 15-4 demonstrates clock rates based on
instruction cycles and the BRG value loaded into
SSPxADD.
EQUATION 15-1:
FCLOCK = _---S---S----P----x---A--F--D--^O--D-^S---^C--+------1---_---_--4----_
FIGURE 15-40: BAUD RATE GENERATOR BLOCK DIAGRAM
SSPxM<3:0>
SSPxADD<7:0>
SSPxM<3:0>
SCLx
Reload
Control
Reload
SSPxCLK
BRG Down Counter
FOSC/2
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.
TABLE 15-4: MSSPx CLOCK RATE W/BRG
FOSC
FCY
BRG Value
FCLOCK
(2 Rollovers of BRG)
32 MHz
8 MHz
13h
400 kHz⁽¹⁾
32 MHz
8 MHz
19h
308 kHz
32 MHz
16 MHz
8 MHz
4 MHz
4Fh
100 kHz
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 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.
DS41412B-page 254
Preliminary
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