Introduction
MOTOROLA
Time Of Day (TOD)
14-3
Preliminary
14
14.1 Introduction
The DSP5685x devices in this manual have a Time Of Day (TOD) feature implemented as
a sequence of counters to track elapsed time. The hardware is capable of tracking time up
to 179.5 years, or 65,535 days.
TOD is comprised of a series of counters tracking elapsed seconds, minutes, hours, and
days. The module requires an input clock ranging from 1-65536Hz integer values only. The
clock is further scaled down to generate a 1Hz clock driving all of the time counters.
All of the time counters are loaded with the time of day upon enabling TOD. Time
counters subsequently track the elapsed time. If required, the TOD feature can issue an
alarm whenever selected current time registers match the time programmed into the
enabled TOD alarm registers. The TOD can also provide an interrupt every second.
An appropriate external clock frequency must be provided and the CGM module must be
configured so TOD clock input in integer HZ from 1-65536Hz is provided. Once
completed, the internal clock prescaler within the TOD module can be configured to
provide a 1Hz time-base clock to the module.
The CGM provides a bit to select one of two external clock prescalers. The oscillator TOD
clock prescaler is a fixed
128 divider. The CGM TOD clock prescaler is a programmable
divider followed by a fixed
2 divider. The programmable portion ranges from divide by 1
up to 2 to the 12th power.
The oscillator prescaler is provided for use with a low frequency (2 - 4MHz) external
clock and it is provided for use in conjunction with the PLL. The CGM clock prescaler
consumes more power and it is larger for use with direct external clock frequencies from
4MHz up to 240MHz.
It is preferable to use the highest frequency TOD clock input possible therefore to do as
much clock division as possible using the internal prescaler within the TOD module. TOD
clock frequencies below 10Hz are not recommended.