Z8 Encore! XP® 4K Series
Product Specification
65
–
If using the Timer Output alternate function, set the initial output level (High or
Low).
2. Write to the Timer High and Low Byte registers to set the starting count value (usually
0001H). This action only affects the first pass in CONTINUOUS mode. After the first
timer Reload in CONTINUOUS mode, counting always begins at the reset value of
0001H.
3. Write to the Timer Reload High and Low Byte registers to set the Reload value.
4. Enable the timer interrupt (if appropriate) and set the timer interrupt priority by
writing to the relevant interrupt registers.
5. Configure the associated GPIO port pin (if using the Timer Output function) for the
Timer Output alternate function.
6. Write to the Timer Control register to enable the timer and initiate counting.
In CONTINUOUS mode, the system clock always provides the timer input. The timer
period is given by the following equation:
Reload Value × Prescale
Continuous Mode Time-Out Period (s) = ---------------------------------------------------------------------------
System Clock Frequency (Hz)
If an initial starting value other than 0001His loaded into the Timer High and Low Byte
registers, use the ONE-SHOT mode equation to determine the first time-out period.
COUNTER Mode
In COUNTER mode, the timer counts input transitions from a GPIO port pin. The timer
input is taken from the GPIO Port pin Timer Input alternate function. The TPOL bit in the
Timer Control Register selects whether the count occurs on the rising edge or the falling
edge of the Timer Input signal. In COUNTER mode, the prescaler is disabled.
The input frequency of the Timer Input signal must not exceed one-fourth the system
clock frequency. Further, the high or low state of the input signal pulse must be no less
than twice the system clock period. A shorter pulse may not be captured.
Caution:
Upon reaching the Reload value stored in the Timer Reload High and Low Byte registers,
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 COUNTER mode and initiating the count are as fol-
lows:
1. Write to the Timer Control register to:
–
–
Disable the timer
Configure the timer for COUNTER mode
PS022815-0206
Timers
ZILOG [ ZILOG, INC. ]
