PIC16F1847_13 Datasheet, PDF (280/440 Pages) Microchip Technology – 18/20/28-Pin Flash Microcontrollers with XLP Technology

PIC16(L)F1847
25.7 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 25-6).
When a write occurs to SSPxBUF, 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 25-40 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 MSSPx is
being operated in.
Table 25-4 demonstrates clock rates based on
instruction cycles and the BRG value loaded into
SSPxADD.
EQUATION 25-1:
FCLOCK = _---S---S----P----x---A--F--D--^O--D-^S---^C--+------1---_---_--4----_
FIGURE 25-40: BAUD RATE GENERATOR BLOCK DIAGRAM
SSPM<3:0>
SSPxADD<7:0>
SSPM<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 25-4: 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.
DS40001453D-page 280
Preliminary
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