Z8F6421PM020SC Datasheet, PDF (98/299 Pages) Zilog, Inc. – High Performance 8-Bit Microcontrollers Z8 Encore-R 64K Series

Z8 Encore!^® 64K Series
Product Specification
78
– 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), affecting only 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. If desired, 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 1 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:
Continuous Mode Time-Out Period (s) = --------R----e---l-o---a---d-----V-----a---l-u----e----^×-----P---r---e---s--c---a---l-e--------
System Clock Frequency (Hz)
If an initial starting value other than 0001H is loaded into the Timer High and Low Byte
registers, the ONE-SHOT mode equation must be used 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 1 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.
Caution:
The input frequency of the Timer Input signal must not exceed one-fourth
the system clock frequency.
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 0001H and 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 1 register to:
– Disable the timer
– Configure the timer for COUNTER mode
PS019915-1005
Timers