Special Bits

i-TRiLOGI contains a number of special purpose bits that are useful for certain applications. These include 8 clock pulses ranging from periods of 0.01 second to 1 minute, a "Normally-ON" flag and a "First Scan Pulse", etc. To use any of these bits, enter the ladder editor and create a "contact"; when the I/O table pops up, scroll the windows until a "Special Bits" menu pops up. This menu is located after the "Counter Table" and before the "Input" table. as shown below:

1. Clock pulse bits

The 8 clock pulses supported by i-TRiLOGI are:

Clock Pulse Period

Ladder Symbol

  0.01 second

  Clk:.01s

  0.02 second

  Clk:.02s

  0.05 second

  Clk:.05s

  0.1 second

  Clk:0.1s

  0.2 second

  Clk:0.2s

  0.5 second

  Clk:0.5s

  1.0 second

  Clk:1.0s

  1 minute

  Clk:1min

A clock pulse bit is ON for the first half of the rated period, then OFF for the second half. Duty cycles for these clock pulse bits are therefore 50%, as follow:

The clock pulse bits are often used with counter instructions to create timers. Additionally, they can be used as timing source for "Flasher" circuit. A reversible counter can also work with a clock pulse bit to create secondary clock pulses of periods that are multiples of the basic clock pulse rate.

2. SeqN:X

These are special "Sequencer" contacts which are activated only when the step counter of a Sequencer N reaches step #X. E.g. a   Normally Open contact Seq2:6 is closed only when Sequencer #2 reaches Step #6. At any other step, this contact is opened. Click this link for detailed explanation and working examples on how to use a Sequencer.

 

3.  Normally ON Flag - Norm.ON

You can make use of this flag if you need to keep something permanently ON regardless of any input conditions. This is because with the exception of Interlock Off function ———[ILoff], a coil or a special function is not allowed to connect directly to the power line (the vertical line on the left end of the ladder diagram). If you need to permanently enable a coil, consider using the "Normally-ON" bit from the "Special Bits" menu, as follow:

ladderref11.gif (723 bytes)

4. First Scan Pulse - 1st.Scan

This special bit will only be turned ON in the very first scan time of the ladder program. After that it will be permanently turned OFF. This is useful if you need to initialize certain conditions at the beginning. When the program is transferred to the PLC, this bit will only be ON when the PLC is first powered up or after it has been reset.

 

5. Real Time Clock Error - RTC.Err

FMD and Nano-10 PLC

This bit is turned ON if an Nano-10 or FMD PLC does not have one of the following installed: FRAM-RTC, FRAM-RTC-0, FRAM-RTC-256 or I2C-FRAM-RTC and the clock has been reset due to power failure or watchdog timer reset. This gives warning to applications that require a correct real world time (such as scheduled ON/OFF operation) that the clock data is incorrect, hence enabling corrective action to be taken.

F-Series PLC

Since the F-Series PLCs do not use the MX-RTC and instead have an on-board batter-backed RTC, the RTC Error event occurs if the RTC is corrupted or damaged (see the F-Series User Manual - section 12.8 for more detail) or if the battery is not installed. The special bit is called RTC.Err and can be obtained from the “Special Bits” I/O Table. The RTC.Err contact can be used to activate an alarm of some kind.

M-Series PLC (Legacy)

This bit is turned ON if the M-series PLC does not have battery-backed MX-RTC option and the clock has been reset due to power failure or watchdog timer reset. This gives warning to applications that require a correct real world time (such as scheduled ON/OFF operation) that the clock data is incorrect, hence enabling corrective action to be taken.