Maple Systems OIT Family - Manual (Page 29)

Function Key LED Coils
The Function Key LEDs (OIT3250, OIT4450, and OIT5400 only) can either be
controlled by the OIT or by a block of discrete coils in the PLC called the Function Key
LED coils. When controlled by the PLC:
• if the corresponding coil is set, the LED is on
• if the corresponding coil is clear, the LED is off.
For more information on LEDs, refer to CHAPTER 8: Using the LEDs.
Register Monitoring
The PLC’s data and coil registers can be monitored, displayed, and updated by the OIT.
This can be done by configuring the OIT screens to display PLC data and coil registers as
embedded data fields (PLC register monitors). When the OIT displays a screen that
contains a PLC register monitor, the OIT reads the specified PLC register address and
then displays the data. If the PLC register monitor has been configured as read/write,
when the operator changes the data in the PLC register monitor on the OIT’s display the
OIT writes the change to the PLC register.
Up to 25 read only or read/write PLC register monitors can be displayed in each OIT
screen. If more than one PLC register monitor is on a screen, each one is updated by the
OIT in continuous succession as rapidly as possible within the constraints of the particular
PLC protocol and baud rate selected. Therefore, the update rate of each PLC register
monitor is determined by the number of PLC register monitors on the screen and the PLC
protocol being used (baud rate, protocol overhead, PLC program, etc.). For more
information on PLC register monitors, refer to CHAPTER 4: PLC Register Monitors.
Performance Considerations
OIT Memory Requirements
The OIT Family Operator Interface Terminals have FLASH memory for storing program
code, protocol code, and system configuration information. These devices are of the latest
technology and permit easy firmware upgrades, protocol enhancements, and safe storage
of important configuration data. Each OIT is capable of storing a maximum of 500
screens (250 screens for the OIT5400).
Data is stored dynamically to get the most out of the memory space allocated for
configuration data. Memory is used only as necessary instead of allocating a certain
number of bytes per message in the OIT. This means that the maximum number of
screens which can actually be created is determined by how many characters the system
programmer places into each screen, how many PLC register monitors are on each
screen, and how many special attributes are used (for example, blinking characters, scroll
lines, etc.). Using this storage technique, it is very difficult to actually use all of the
available memory in a single application.
The OIT Memory Used bar graph in the OITware-200 main screen keeps the system
programmer informed of the remaining memory at all times.
Operational Overview 29
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