
Clocks and Power Control
MOTOROLA
MPC801 USER’S MANUAL
5-3
5
5.1 THE CLOCK MODULE
The MPC801 clock module consists of the main crystal oscillator, the SPLL, low-power
divider, clock generator/driver blocks, and clock module/system low-power control block.
The clock module and system low-power control block receives control bits from the system
clock control register, the PLL, the low-power and reset control register, and the reset status
register. To improve noise immunity, the charge pump and the VCO of the SPLL have their
own set of power supply pins (VDDSYN and VSSSYN), whereas KAPWR and VSS power
the following clock unit modules.
Oscillator
pitrtclk and tmbclk generation logic
DB
Decrementer
Real-time clock
Periodic interrupt timer
System clock and reset control register (SCCR)
PLL low-power and reset control register (PLLRCR)
Reset status register (RSR)
All other circuits are powered by the normal supply pins—VDDH/VDDL and VSS. VDDH
feeds the I/O buffers and logic and VDDL supplies the internal chip logic to reduce system
power consumption. However, the power supply connected to VDDH should be at least as
big as the one connected to VDDL. The power supply for each block is listed in Table 5-1
and described in
Section 5.9 Basic Power Structure
.
Table 5-1. MPC801 Power Supply
VDDH
VDDL
VDDSYN
KAPWR
I/O Pad Logic
X
CLKOUT
X
SPLL (Digital)
X
Clock Block
X
Internal Logic
X
Clock Drivers
X
SPLL (Analog)
X
Main Oscillator
X
SCCR, PLLRCR and RSR
X
RTC, PIT, TB, and DEC
X
NOTE: X
denotes that the power supply is used.