ADLINK ACL-8454/12 - Manual (Page 28)

20 • Installation & Configurations
The timer/counter output signals (COUT n) of 8254 are controlled by clock
source, gate control and software program. All the outputs of the 8
independent counters are sent to the 37 pins connector directly. The
COUT6 and COUT12 of the two pairs of cascaded counters are also sent to
connector. Therefore, totally 10 counter outputs are sent to connector, see
'Pin assignment' for corresponding signal pin number.
In addition, the output-signals may be used as clock sources or gate
controls of the cascaded counters, see the above sections. It is possible to
cascaded two counters by jumpers. The counters output COUT6, COUT12
are also used as internal interrupt source (refers to 'Interrupt System').
2.12 Interrupt System
The ACL-8454 has two interrupt sources on board. That means the two
interrupt levels or two IRQ lines can be used by this board. The block
diagram of the interrupt system is shown in Figure 2.15.
The two IRQ channels can be set by jumper JP1 and JP2 respectively. The
high IRQ level is jumper wired to IRQ 10~15 and the low IRQ level is jumper
wired to IRQ 3~9. The source of the high IRQ level comes from /COUT6
which is the reversed output of cascaded counters.
The reversed COUT6 interrupt is very useful because the /COUT6 is also
send to the gate control of counter #1 ~ #4 for frequency measurement.
While /COUT6 is high, the frequency measurement is counting. When
/COUT6 goes low, the counting is ending and an interrupt is generated from
interrupt system so that the software can sample and memorize the result of
frequency measurement. In watchdog application, using reversed COUT6
has no problems because the frequency of COUT6 and reversed COUT6 is
the same.
The sources of the low IRQ level come from internal (COUT12) or external
(ECLK10) source which are jumper selectable by JP3. Note the COUT12 is
not reversed counter output.
Note: The IRQ channels must not conflict with other add-on cards on
your PC.