ADLINK PCI-7442 - Manual (Page 43)

Operation theory 31
3.4 Watchdog timer (WDT)
In safety-critical applications, you can enable the watchdog timer
(WDT) function to automatically generate an interrupt signal, in
case the operating system or the PCI-7442/PCI-7444 card
crashes. To access this function, you must first configure the
watchdog timer overflow counter by windows API. Generally, the
trigger source would come from the onboard 32-bit watchdog
timer.
The WDT overflow interval can be programmed through API. You
must reload the WDT counter value before enabling the WDT.
After enabling the watchdog timer, you must periodically reload the
timer value by software command. If the timer is not being
reloaded within the specified interval, the WDT module generates
an overflow interruption signal. When you enable the
SafetyOut_Enable bit, the PCI-7442/PCI-7444 would automati-
cally configure the 64-CH/128-CH DO safety statuses. This WDT
function is disabled by default.
3.5 Programmable TTL Input/Output
The PCI-7442/7443/7444 card provides a 32-CH programmable
TTL input/output. These channels are divided between two con-
nectors: JP3 and JP4. You can change the direction of each TTL
channel any time. The I/O voltage level suits with 5 V TTL level
and 3.3 V TTL level. But the driving strength of each channel is 4
mA. Pay particular attention to the current consumption of the TTL
channel.