The MSSP module has a Baud Rate Generator (BRG) available for clock generation in both I2C and SPI Host modes. The BRG reload value is placed in the SSPxADD register. When a write occurs to SSPxBUF, the BRG will automatically begin counting down. MSSP Baud Rate Generator Frequency Equation shows how the value for SSPxADD is calculated.
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 Reload signal, shown in Figure 1, triggers the value from SSPxADD to be loaded into the BRG counter. This occurs twice for each oscillation of the module clock line.
Table 1 illustrates clock rates based on instruction cycles and the BRG value loaded into SSPxADD.
MSSP Baud Rate Generator Frequency Equation
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 (2 Rollovers of BRG) |
|---|---|---|---|
| 32 MHz | 8 MHz | 13h | 400 kHz |
| 32 MHz | 8 MHz | 19h | 308 kHz |
| 32 MHz | 8 MHz | 4Fh | 100 kHz |
| 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 |
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Note: Refer to
the I/O port electrical specifications in the “Electrical
Specifications” chapter, Internal Oscillator Parameters, to ensure
the system is designed to support all requirements.
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