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ControlLogix 7252 LDT Interface Manual
Revision 1.5
Output Registers: (Data sent from the PLC to the 7252 module)
The output registers are used to execute commands that typically occur during machine operation, while module setup
functions are accomplished with the use of Message Instructions. See chapter 3 and 4 for configuring the 7252 module.
1 Channel configuration
Channel
Number
32 Bit
Word
Function
1
0
Command Bits
1
Interpolation CST Value
2 Channels configuration
Channel
Number
32 Bit
Word
Function
1
0
Command Bits
1
Interpolation CST Value
2
2
Command Bits
3
Interpolation CST Value
Command Bits for channels 1 & 2:
Bit 0: APPLY PRESET COMMAND: The 0 to 1 transition of this bit changes the respective EnDat channel’s Data
Value to the Preset Value that was programmed with the channels Setup Message Instruction. The Default
Preset Value is zero.
Bit 1: INTERPOLATION COMMAND: Both transitions of this bit, (0 to 1) and (1 to 0), causes the respective
EnDat channel to read the Current System Time from the output register and calculate the Interpolated Data
Value. This Interpolated Data Value will be read by the PLC during the next RPI update of the module.
Bit 2:CLEAR LATCHED TRANSDUCER FAULTS: A 0 to 1 transition of this bit will clear a Latched
Transducer Fault Error message.
Bits 3 to 31: Reserved for future use
Apply Preset Programming Cycle
1.
The ladder logic program sets the APPLY PRESET COMMAND bit when you want to change the channel’s
current Data Value to the previously programmed Preset Value.
2.
The 7252 module will set the APPLY PRESET ACKNOWLEDGE bit in the input registers to indicate that it
has received the command.
3.
When the ladder logic program sees that the APPLY PRESET ACKNOWLEDGE bit is set, it will reset the
APPLY PRESET COMMAND bit. The programming cycle is now complete.
The 7252 module’s Flash memory is guaranteed for 10,000 write cycles before
writing to it will cause it to fault. Therefore continuously applying the Preset should
be avoided. If your application requires you to continuously apply the Preset,
consider calculating and applying the Preset in your PLC program.
Programming the 7252’s setup parameters will reset the internal offset
generated by an Apply Preset operation. If you are programming the unit’s
setup parameter at every power up, this may be the reason that your data value
to not be absolute through power down.
