Programming instructions

50
If STL programming is utilized in conjunction with the IST instruction (Initial
State) causes certain state relays to have special operations. 2 examples
are: S0 is the manual operation return state and S2 is the automatic
operation return state.
One last use of state relays is as a fault annunciator. Through
programming techniques described in chapter 4.4 of the FX3U
Programming Manual, S900 ~ S999 can be used as user defined fault
indicators.
T - Timers
T devices are timer devices by default timers are either 100msec time
increments, 10msec time increments, or 1msec time increments
depending on the timer address. Most timers, depending on their address,
are non-retentive, meaning they do not hold their current value if the input
conditions stop conducting. In the FX2N, FX, FX2NC, timers with
addresses T246 and above are retentive. This means the timer hold its
value until it is reset. Retentive timers have a time base of either 100msec
or 1msec, depending on the address.
When a timer reaches the associated preset value the T device coil is
energized, the corresponding T device contact becomes active also. All
timers are 16 bit, meaning the maximum preset is +32767. Valid presets
are K values and D data registers. For a 100msec timer the maximum
time is 3276.7 seconds.
In GX-Developer, it is possible to assign a range of timers to be battery-
backed. This means the timers will hold their accumulated value in the
event of a power loss – provided the logic that drives the rung is battery-
backed as well. Otherwise the timer will be reset.
C - Counters
C devices are counter devices. The standard is all counters are retentive,
holding their current count until reset. In GX-Developer you can assign
counters to be battery-backed. When a counter reaches the associated
preset value, the C device coil is energized, the corresponding C device
contacts become active also. Counters can be 16 or 32 bit, meaning the
maximum count range is –32768 to +32767 (16 bit) or -2,147,483,648 to
2,147,483,647 (32 bit). Negative presets are not very useful, as will be
explained in more detail in Lesson 12. Valid presets are K values and D
data registers.
There are 3 types of counters: 16 bit up counters, 32 bit up/down
counters, and 32 bit high-speed counters. Within the high-speed counter
category there are 1 phase, 2 phase, and A/B phase counters.
Counters will be covered in more detail in the chapter on Timers and
Counters.