
C165H
Architectural Overview
Data Sheet
44
2001-04-19
PRELMNARY
by 128. The high byte of the Watchdog Timer register can be set to a prespecified reload
value (stored in WDTREL) in order to allow further variation of the monitored time
interval. Each time it is serviced by the application software, the high byte of the
Watchdog Timer is reloaded.
-EXCERPT-
The five 16-bit timers are organized in two separate modules, GPT1 and GPT2. Each
timer in each module may operate independently in a number of different modes, or may
be concatenated with another timer of the same module.
Each timer can be configured individually for one of three basic modes of operation,
which are Timer, Gated Timer, and Counter Mode. In Timer Mode the input clock for a
Counter Mode allows a timer to be clocked in reference to external events (via TxIN).
Pulse width or duty cycle measurement is supported in Gated Timer Mode where the
operation of a timer is controlled by the ‘gate’ level on its external input pin TxIN.
The count direction (up/down) for each timer is programmable by software or may
additionally be altered dynamically by an external signal (TxEUD) to facilitate eg. position
tracking.
The core timers T3 and T6 have output toggle latches (TxOTL) which change their state
on each timer over-flow/underflow. The state of these latches may be output on port pins
(TxOUT) or may be used internally to concatenate the core timers with the respective
auxiliary timers resulting in 32/33-bit timers/counters for measuring long time periods
with high resolution.
Various reload or capture functions can be selected to reload timers or capture a timer’s
contents triggered by an external signal or a selectable transition of toggle latch TxOTL.
Watchdog Timer
The Watchdog Timer represents one of the fail-safe mechanisms which have been
implemented to prevent the controller from malfunctioning for longer periods of time.
The Watchdog Timer is always enabled after a reset of the chip, and can only be
disabled in the time interval until the EINIT (end of initialization) instruction has been
executed. Thus, the chip’s start-up procedure is always monitored. The software has to
be designed to service the Watchdog Timer before it overflows. If, due to hardware or
software related failures, the software fails to do so, the Watchdog Timer overflows and
generates an internal hardware reset and pulls the RSTOUT pin low in order to allow
external hardware components to reset.
The Watchdog Timer is a 16-bit timer, clocked with the CPU clock divided either by 2 or
3.5
Protected Bits
The C165H provides a special mechanism to protect bits which can be modified by the
on-chip hardware from being changed unintentionally by software accesses to related
bits (see also chapter “The Central Processing Unit”).