mc68hc05pl4b Freescale Semiconductor, Inc, mc68hc05pl4b Datasheet - Page 49

• Manufacturer Part Number: mc68hc05pl4b
• Description: Low-cost Single-chip Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

8.1
MC68HC05PL4
REV 2.0
This section describes the system clock options for the MC68HC05PL4.
SYSTEM CLOCK SOURCE AND FREQUENCY OPTION
The operating bus frequency of the MCU is dependent on the clock source (OSC1
or internal RC) and the clock divider ratio. These are selected in the System Clock
Control Register (SYSCR).
SYSDIV1,SYSDIV2 — System Clock Divider Select
CKSEL1,CKSEL2 — System Clock Source Select
The CKSEL1 and CKSEL2 bits select the system clock source for the MCU. After
power-on-reset, the default setting is internal RC. Table 8-2 shows the system
clock source options.
SYSCR
$001D
The SYSDIV1 and SYSDIV2 bits select the divide ratio for the clock source.
After power-on-reset, the default setting is divide by 2. Table 8-1 shows the
divide ratios.
POR
W
R
CKSEL1
SYSDIV1 SYSDIV2
0
0
1
1
Figure 8-1. System Clock Control Register (SYSCR)
BIT 7
0
Freescale Semiconductor, Inc.
Table 8-1. System Clock Divider Select
Table 8-2. System Clock Source Select
For More Information On This Product,
SYSDIV1
CKSEL2
BIT 6
0
0
1
1
0
0
1
0
1
SYSTEM CLOCKS
Go to: www.freescale.com
SYSTEM CLOCKS
CKSEL1
SECTION 8
BIT 5
April 30, 1998
SYSDIV2
1
External from OSC1 (with RC enabled)
0
1
0
1
CKSEL2
BIT 4
0
External from OSC1
External from OSC1
Select Option
Internal RC
FMODE
GENERAL RELEASE SPECIFICATION
BIT 3
DIV
16
1
2
4
8
OSCF
BIT 2
0
BIT 1
RCF
1
CKOSC
BIT 0
0
8-1