EZ80L92MCU Datasheet, PDF (92/241 Pages) Zilog, Inc. – eZ80Acclaim Flash Microcontrollers

eZ80L92 MCU
Product Specification
77
Programmable Reload Timer Operation
Setting Timer Duration
There are three factors to consider when determining Programmable Reload Timer dura-
tion—clock frequency, clock divider ratio, and initial count value. Minimum duration of
the timer is achieved by loading 0001h. Maximum duration is achieved by loading
0000h, because the timer first rolls over to FFFFh and then continues counting down to
0000h.
The time-out period of the PRT is returned by the following equation:
Clock Divider Ratio x Reload Value
PRT Time-Out Period =
System Clock Frequency
To calculate the time-out period with the above equation when using an initial value of
0000h, enter a reload value of 65536 (FFFFh + 1).
Minimum time-out duration is 4 times longer than the input clock period and is generated
by setting the clock divider ratio to 1:4 and the reload value to 0001h. Maximum time-out
duration is 2²⁴ (16,777,216) times longer than the input clock period and is generated by
setting the clock divider ratio to 1:256 and the reload value to 0000h.
SINGLE PASS Mode
In SINGLE PASS mode, when the end-of-count value, 0000h, is reached, counting halts,
the timer is disabled, and the PRT_EN bit resets to 0. To restart the timer, the CPU must
reenable the timer by setting the PRT_EN bit to 1. An example of a PRT operating in SIN-
GLE PASS mode is illustrated in Figure 19. Timer register information is indicated in
Table 29.
CLK
CLKEN
IOWRN
t _CNTH7:0]
t _CNTL7:0]
IRQ
0
0
4
3
2
1
0
Figure 19. PRT Single Pass Mode Operation Example
PS013012-1004
PRELIMINARY
Programmable Reload Timers