snap ethernet-based i/o units protocols and programming guide

CHAPTER 2: OVERVIEW OF PROGRAMMING
level in Vat #12 (if the temperature reaches 48 °C, bit 1 is turned on). Bit 2 might indicate the
status of Pump A (if the pump is off, the bit is off; if the pump is on, the bit is on).
Because you can use Scratch Pad bits to keep track of digital and serial events and analog and
digital alarms, you can set up reactions based on a variety of digital, analog, and serial
conditions. In the example above, you could set up a reaction that sends a stream packet if bit 1
is on and bit 2 is off.
Types of Events, Alarms, and Reactions
You can configure the brain to recognize one or a combination of the following as an event:
The state of a digital point (on or off)
A specific high or low value of an analog point, in Engineering Units
A specific number on a digital counter or a high or low number on a quadrature counter
An analog point value or a quadrature counter that is outside an allowable range
The state of a bit in the Scratch Pad (on or off)
A specific string received by a serial module.
You can also set up the brain to react automatically to an event in any or all of the following ways:
Turning digital points on or off (on the same brain)
Turning digital points on or off (on a different brain)
Copying data from one memory map location to another on the same or a different brain
Logging data
Turning a bit in the Scratch Pad on or off
Sending a stream packet
Sending an email message
Sending a string through a serial module to a serial device
Sending an SNMP trap.
In addition, you can use a timer to set up a delay between when the event occurs and the reaction
takes place.
NOTE: At present, it is not possible to set up an automatic analog reaction.
The following table shows steps you would use to configure possible events and reactions to
occur either immediately or after a delay. Page numbers refer you to the memory map addresses
in Appendix A that you would use for configuration. Also, see explanations on the pages
following this table for important information you’ll need to set up events and reactions.
SNAP Ethernet-Based I/O Units Protocols and Programming Guide 27