Datasheet

MC68HC812A4 Data Sheet, Rev. 7
Freescale Semiconductor 101
Chapter 10
Clock Module
10.1 Introduction
Clock generation circuitry generates the internal and external E-clock signals as well as internal clock
signals used by the CPU and on-chip peripherals. A clock monitor circuit, a computer operating properly
(COP) watchdog circuit, and a periodic interrupt circuit are also incorporated into the MCU.
10.2 Block Diagram
Figure 10-1. Clock Module Block Diagram
10.2.1 Clock Generators
The clock module generates four types of internal clock signals derived from the oscillator:
1. T-clocks — Drives the CPU
2. E-clock — Drives the bus interfaces, BDM, SPI, and ATD
3. P-clock — Drives the bus interfaces, BDM, SPI, and ATD
4. M-clock — Drives on-chip modules such as the timer, SCI, RTI, COP, and restart-from-stop delay
time
0:1:1
EXTALXTAL
0:0:0
0:0:1
0:1:0
1:0:0
1:0:1
1:1:0
1:1:1
SYSCLK
ECLK
PCLK
MCLK
TCLK
÷ 2
÷ 2
÷ 2
÷ 2
÷ 2
÷ 2
÷ 2
÷ 2
OSCILLATOR
PHASE-LOCK
LOOP
PLLS
TO CPU
T-CLOCK
GENERATOR
E- AND P-CLOCK
GENERATOR
MUXCLK
0:0
0:1
1:0
÷ 2
÷ 2
÷ 2
REGISTER: CLKCTL
BITS: MCS[B:A]
REGISTER: CLKCTL
BITS: BCS[C:B:A]
TO BDM,
BUSES,
SPI,
ATD
TO SCI, TIM,
PA, RTI, COP
1:1
÷ 2