Z8 Encore! XP® 4K Series
Product Specification
64
it is appropriate to have the Timer Output make a state change at a One-Shot time-out
(rather than a single cycle pulse), first set the TPOL bit in the Timer Control Register to
the start value before enabling ONE-SHOT mode. After starting the timer, set TPOLto the
opposite bit value.
The steps for configuring a timer for ONE-SHOT mode and initiating the count are as fol-
lows:
1. Write to the Timer Control register to:
–
–
–
–
Disable the timer
Configure the timer for ONE-SHOT mode.
Set the prescale value.
Set the initial output level (High or Low) if using the Timer Output alternate
function.
2. Write to the Timer High and Low Byte registers to set the starting count value.
3. Write to the Timer Reload High and Low Byte registers to set the Reload value.
4. If appropriate, enable the timer interrupt and set the timer interrupt priority by writing
to the relevant interrupt registers.
5. If using the Timer Output function, configure the associated GPIO port pin for the
Timer Output alternate function.
6. Write to the Timer Control register to enable the timer and initiate counting.
In ONE-SHOT mode, the system clock always provides the timer input. The timer period
is given by the following equation:
(Reload Value – Start Value) × Prescale
One-Shot Mode Time-Out Period (s) = ------------------------------------------------------------------------------------------------
System Clock Frequency (Hz)
CONTINUOUS Mode
In CONTINUOUS mode, the timer counts up to the 16-bit Reload value stored in the
Timer Reload High and Low Byte registers. The timer input is the system clock. Upon
reaching the Reload value, the timer generates an interrupt, the count value in the Timer
High and Low Byte registers is reset to 0001Hand counting resumes. Also, if the Timer
Output alternate function is enabled, the Timer Output pin changes state (from Low to
High or from High to Low) at timer Reload.
The steps for configuring a timer for CONTINUOUS mode and initiating the count are as
follows:
1. Write to the Timer Control register to:
–
–
–
Disable the timer
Configure the timer for CONTINUOUS mode.
Set the prescale value.
PS022815-0206
Timers
ZILOG [ ZILOG, INC. ]
