
C165H
Architectural Overview
Data Sheet
40
2001-04-19
PRELMNARY
maximum number of operations to be performed in parallel and allows peripherals to be
added or deleted from family members without modifications to the core. Each functional
block processes data independently and communicates information over common
buses. Peripherals are controlled by data written to the respective Special Function
Registers (SFRs). These SFRs are located either within the standard SFR area
(00’FE00
H
...00’FFFF
H
) or within the extended ESFR area (00’F000
H
...00’F1FF
H
).
These built in peripherals either allow the CPU to interface with the external world, or
provide functions on-chip that otherwise were to be added externally in the respective
system.
-EXCERPT-
Prescaler Operation
When pins P0.15-13 (P0H.7-5) are equal ’001’ during reset the CPU clock is derived
from the internal oscillator (input clock signal) by a 2:1 prescaler (see
Table 9
).
The frequency of f
CPU
is half the frequency of f
XTAL
and the high and low time of f
CPU
(ie.
the duration of an individual TCL) is defined by the period of the input clock f
XTAL
.
therefore can be calculated using the period of f
XTAL
for any TCL.
Direct Drive
When pins P0.15-13 (P0H.7-5) equal ’011’ during reset the clock system is directly
driven from the internal oscillator with the input clock signal, ie. f
OSC
= f
CPU
.
The maximum input clock frequency depends on the clock signal’s duty cycle, because
the minimum values for the clock phases (TCLs) must be respected.
Oscillator Watchdog
The C165H provides an Oscillator Watchdog (OWD) which monitors the clock signal
generated by the on-chip oscillator (either with a crystal or via external clock drive) in
prescaler or direct drive mode. For this operation the PLL provides a clock signal which
is used to supervise transitions on the oscillator clock. This PLL clock is independent
from the XTAL1 clock. When the expected oscillator clock transitions are missing the
OWD activates the PLL Unlock / OWD interrupt node and supplies the CPU with the PLL
clock signal. Under these circumstances the PLL will oscillate with its basic frequency.
The OWD’s interrupt output can be disabled by setting bit OSCENBL = '0' (default after
reset) in SYSCON register. In this case no oscillator watchdog interrupt request is
generated and the CPU clock signal is derived from the oscillator clock in any case
Note:
The CPU clock source is only switched back to the oscillator clock after a
hardware reset.
3.4
On-Chip Peripheral Blocks