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A
Model 341 PLC system, this plug must be installed on the unused connector on the last
I/Oexpansion cable in the I/O bus chain.
Timer
A function block that can be used to control the operating cycle of other devices by a
preset and accumulated time interval.
User Memory
The portion of system memory in which the application program and data is stored.
This memory is battery-backed CMOS RAM.
User Reference Type
A reference assigned to data which indicates the memory in which it is stored in the
PLC. References can be either bit-oriented (discrete) or word-oriented (register).
Verify
A function used to compare program configuration and reference data between the CPU
and memory card or EEPROM.
Volatile Memory
A type of memory that will lose the information stored in it if power is removed from
the memory devices. Requires a backup battery for retention of contents of memory. In
the Series 90-30 PLC a Lithium battery is used for this purpose.
Watchdog Timer
A timer in the CPU used to ensure that certain hardware conditions are met within a
predetermined time. The watchdog timer value in the Series 90-30 PLC is 200
milliseconds.
Word
A measurement of memory length, usually 4, 8, or 16-bits long; in the Series 90 PLCs, a
word is 16-bits in length.
Write
To transfer, record, or copy data from one storage device to another, for example, from
CPU to memory card or EEPROM.
A-10
Hand-Held Programmer for Series 90-30/20/Micro Programmable Controllers User’s Manual - February 1996
GFK-0402G