Advance Information
MC68HC908MR16/MC68HC908MR32
—
Rev. 5.0
116
Clock Generator Module (CGM)
MOTOROLA
Clock Generator Module (CGM)
These conditions apply when the PLL is in automatic bandwidth control
mode:
The ACQ bit (see
8.6.2 PLL Bandwidth Control Register
) is a
read-only indicator of the mode of the filter. For more information,
see
8.4.2.2 Acquisition and Tracking Modes
.
The ACQ bit is set when the VCO frequency is within a certain
tolerance,
TRK
, and is cleared when the VCO frequency is out of
a certain tolerance,
UNT
. For more information, see
8.9 Acquisition/Lock Time Specifications
.
The LOCK bit is a read-only indicator of the locked state of the
PLL.
The LOCK bit is set when the VCO frequency is within a certain
tolerance,
Lock
, and is cleared when the VCO frequency is out of
a certain tolerance,
UNL
. For more information, see
8.9 Acquisition/Lock Time Specifications
.
CPU interrupts can occur if enabled (PLLIE = 1) when the PLL
’
s
lock condition changes, toggling the LOCK bit. For more
information, see
8.6.1 PLL Control Register
.
The PLL also may operate in manual mode (AUTO = 0). Manual mode
is used by systems that do not require an indicator of the lock condition
for proper operation. Such systems typically operate well below f
BUSMAX
and require fast startup. These conditions apply when in manual mode:
ACQ is a writable control bit that controls the mode of the filter.
Before turning on the PLL in manual mode, the ACQ bit must be
clear.
Before entering tracking mode (ACQ = 1), software must wait a
given time, t
ACQ
(see
8.9 Acquisition/Lock Time
Specifications
), after turning on the PLL by setting PLLON in the
PLL control register (PCTL).
Software must wait a given time, t
AL
, after entering tracking mode
before selecting the PLL as the clock source to CGMOUT
(BCS = 1).
The LOCK bit is disabled.
CPU interrupts from the CGM are disabled.