Z8F042ASJ020EG2156 Datasheet, PDF (96/280 Pages) Zilog, Inc. – High-Performance 8-Bit Microcontrollers

Z8 Encore! XP^® F082A Series
Product Specification
80
6. Configure the associated GPIO port pin for the Timer Input alternate function.
7. Write to the Timer Control Register to enable the timer and initiate counting.
In Capture Mode, the elapsed time from timer start to Capture event can be calculated
using the following equation:
Capture Elapsed Time (s) = -^--^C----^a---^p---^t--^u---^r-^e-----^V----^a---^l-^u---^e----^–-----^S----^t-^a---^r--^t---^V----^a---^l-^u---^e---^----^----^P---^r--^e---^s---^c---^a---^l-^e-
System Clock Frequency (Hz)
Capture Restart Mode
In Capture Restart Mode, the current timer count value is recorded when the acceptable
external Timer Input transition occurs. The Capture count value is written to the Timer
PWM High and Low Byte registers. The timer input is the system clock. The TPOL bit in
the Timer Control Register determines if the Capture occurs on a rising edge or a falling
edge of the Timer Input signal. When the Capture event occurs, an interrupt is generated
and the count value in the Timer High and Low Byte registers is reset to 0001h and count-
ing resumes. The INPCAP bit in TxCTL0 Register is set to indicate the timer interrupt is
because of an input capture event.
If no Capture event occurs, the timer counts up to the 16-bit Compare value stored in the
Timer Reload High and Low Byte registers. Upon reaching the reload value, the timer
generates an interrupt, the count value in the Timer High and Low Byte registers is reset to
0001h and counting resumes. The INPCAP bit in TxCTL0 Register is cleared to indicate
the timer interrupt is not caused by an input capture event.
Observe the following steps for configuring a timer for Capture Restart Mode and initiat-
ing the count:
1. Write to the Timer Control Register to:
– Disable the timer
– Configure the timer for Capture Restart Mode by writing the TMODE bits in the
TxCTL1 Register and the TMODEHI bit in TxCTL0 Register
– Set the prescale value
– Set the Capture edge (rising or falling) for the Timer Input
2. Write to the Timer High and Low Byte registers to set the starting count value (typi-
cally 0001h).
3. Write to the Timer Reload High and Low Byte registers to set the reload value.
4. Clear the Timer PWM High and Low Byte registers to 0000h. This allows the soft-
ware to determine if interrupts were generated by either a capture event or a reload. If
the PWM High and Low Byte registers still contain 0000h after the interrupt, the
interrupt was generated by a Reload.
PS022828-0413
PRELIMINARY
Operation