PIC32MX440F256H-80I Datasheet, PDF (533/646 Pages) Microchip Technology – 64/100-Pin General Purpose and USB 32-Bit Flash Microcontrollers

23.6 Peripheral Bus Scaling Method
Most of the peripherals on the device are clocked using
the PBCLK. The peripheral bus can be scaled relative
to the SYSCLK to minimize the dynamic power con-
sumed by the peripherals. The PBCLK divisor is con-
trolled by PBDIV<1:0> (OSCCON<20:19>), allowing
SYSCLK-to-PBCLK ratios of 1:1, 1:2, 1:4, and 1:8. All
peripherals using PBCLK are affected when the divisor
is changed. Peripherals such as the Interrupt Control-
ler, DMA, Bus Matrix, and Prefetch Cache are clocked
directly from SYSCLK, as a result, they are not affected
by PBCLK divisor changes.
Most of the peripherals on the device are clocked using
the PBCLK. The peripheral bus can be scaled relative
to the SYSCLK to minimize the dynamic power con-
sumed by the peripherals. The PBCLK divisor is con-
trolled by PBDIV<1:0> (OSCCON<20:19>), allowing
SYSCLK-to-PBCLK ratios of 1:1, 1:2, 1:4, and 1:8. All
peripherals using PBCLK are affected when the divisor
is changed. Peripherals such as USB, Interrupt Con-
troller, DMA, Bus Matrix, and Prefetch Cache are
clocked directly from SYSCLK, as a result, they are not
affected by PBCLK divisor changes
Changing the PBCLK divisor affects:
• The CPU to peripheral access latency. The CPU
has to wait for next PBCLK edge for a read to
complete. In 1:8 mode this results in a latency of
one to seven SYSCLKs.
• The power consumption of the peripherals. Power
consumption is directly proportional to the fre-
quency at which the peripherals are clocked. The
greater the divisor, the lower the power consumed
by the peripherals.
To minimize dynamic power the PB divisor should be
chosen to run the peripherals at the lowest frequency
that provides acceptable system performance. When
selecting a PBCLK divider, peripheral clock require-
ments such as baud rate accuracy should be taken into
account. For example, the UART peripheral may not be
able to achieve all baud rate values at some PBCLK
divider depending on the SYSCLK value.
PIC32MX3XX/4XX
© 2008 Microchip Technology Inc.
Preliminary
DS61143E-page 531