PIC16F1459-ESOSQTP datasheet(66/418 Pages) MICROCHIP

66 / 418 page

PIC16(L)F1454/5/9

DS41639A-page 66

Preliminary

 2012 Microchip Technology Inc.

5.3

CPU Clock Divider

The CPU Clock divider allows the system clock to run

at a slower speed than the Low/Full-Speed USB

module clock, while sharing the same clock source.

Only the oscillator defined by the settings of the FOSC

bits of the Configuration Words may be used with the

CPU clock divider. the CPU clock divider is controlled

by the CPUDIV<1:0> bits of the Configuration Words.

Setting the CPUDIV bits will set the system clock to:

• Equal the clock speed of the USB module

• Half the clock speed of the USB module

• One third the clock speed of the USB Module

• One sixth clock speed of the USB module

For more information on the CPU Clock Divider, see

Figure 5-1 and Configuration Words.

5.4

USB Operation

The USB module is designed to operate in two different

modes:

• Low Speed

• Full Speed

To achieve the timing requirements imposed by the

USB specifications, the internal oscillator or the primary

external oscillator are required for the USB module.

The FOSC bits of the Configuration Words must be set

to INTOSC, ECH or HS mode with a clock frequency of

6, 12, or 16 MHz.

5.4.1

LOW-SPEED OPERATION

For low-speed USB Operation, a 24 MHz clock is

required for the USB module. To generate the 24 MHz

clock, the following Oscillator modes are allowed:

• HFINTOSC with PLL

• ECH mode

•HS mode

Table 5-1 shows the recommended Clock mode for

low-speed operation.

5.4.2

HIGH-SPEED OPERATION

For full-speed USB operation, a 48 MHz clock is

required for the USB module. To generate the 48 MHz

clock, the following oscillator modes are allowed:

• HFINTOSC with PLL

• ECH mode

•HS mode

Table 5-1 shows the recommended Clock mode for

full-speed operation.

TABLE 5-1:

LOW-SPEED USB CLOCK SETTINGS

Clock Mode

Clock

Frequency

PLL Value

USBLSCLK

CPUDIV<1:0>

System Clock

Frequency

(MHz)

HFINTOSC

16 MHz

8 MHz

ECH or HS mode

16 MHz

12 MHz

8 MHz

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