PIC16LF1454 Datasheet, PDF (66/418 Pages) Microchip Technology – 14/20-Pin Flash, 8-Bit USB Microcontrollers with XLP Technology

PIC16(L)F1454/5/9
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
16 MHz
3x
1
HFINTOSC
8 MHz
3x
0
16 MHz
3x
1
ECH or HS mode
12 MHz
4x
1
8 MHz
3x
0
CPUDIV<1:0>
11
10
01
00
11
10
01
00
11
10
01
00
11
10
01
00
11
10
01
00
System Clock
Frequency
(MHz)
8
16
24
48
4
8
12
24
8
16
24
48
8
16
24
48
4
8
12
24
DS41639A-page 66
Preliminary
 2012 Microchip Technology Inc.