Macros 17 and 18 use maintained clockwise and counterclockwise commands on supported G120 variants. Their handling of direction changes and overlapping commands differs. Select the behavior deliberately and verify it against the firmware-specific timing diagram.
What two-wire control means
A maintained contact or PLC output requests operation while it remains active. This differs from a momentary start pushbutton that initiates a latched run state. The term describes the command method; it does not mean the entire installation needs only two conductors.
In the referenced CU240E-2 preset, DI0 requests ON/OFF1 right, DI1 requests ON/OFF1 left and DI2 acknowledges faults. The analogue input supplies the speed reference. Confirm the actual terminal numbers from the control-unit drawing rather than copying a drawing from another G120 family.
Use this arrangement when the machine controller can maintain a clear direction request and remove it on a normal stop. Design restart permission separately, including what happens after the PLC restarts, a drive fault clears or supply returns.
The important difference between macros 17 and 18
| Behavior | Macro 17 / direction method 1 | Macro 18 / direction method 2 |
|---|---|---|
| No direction requested | Normal stop request | Normal stop request |
| One direction active | Requested direction | Requested direction |
| New direction while moving | New command accepted only at standstill | New command can be accepted while moving |
| Both direction signals high | First command determines direction | Stop request |
The macro numbers are interface presets; the corresponding two-wire function selection is commonly represented by p3334 values 1 and 2. The cited function descriptions explain the behavior. Check the resulting online connections, because a previously modified project may no longer match its original preset.
Do not use overlapping direction commands as the routine stopping method. Make the PLC request unambiguous. For an application that must stop before reversing, implement and test that sequence explicitly rather than relying on the operator to time two switches.
Prepare the terminal and PLC command design
- Record the drive variant, firmware, active data set and current project backup.
- Define normal stop, direction permission and restart conditions in the control description. Keep the independent safety function intact.
- Select the supported macro through basic commissioning and inspect the resulting command and reference connections.
- With power isolated, wire the input group according to its polarity and common arrangement. Use the exact control-unit terminal diagram.
- With motion prevented, verify each physical input in r0722. Check that the PLC output and drive input change together.
- Use an approved low reference for the first motion test. Confirm each permitted direction and normal stop before trying any sequence change.
An ordinary interlock in standard PLC logic does not replace a safety-rated function. It is useful for avoiding contradictory requests, but its role and failure behavior should be stated in the machine documentation.
Practical lab: log a direction-change sequence
Create a watch table containing forward request, reverse request, the two observed drive inputs, speed request, actual speed and drive status. Start with both commands inactive. Request one direction, remove the request and observe the ramp to standstill. Then repeat in the other permitted direction.
For a machine approved for dynamic reversal, compare the requested behavior against the selected method using a controlled test. For machinery that cannot reverse safely, verify command handling with motion inhibited and do not perform a loaded reversal just to demonstrate the macro.
Record timestamps or a trace where available. A screenshot of the final input state cannot show which contact became active first. This matters when diagnosing the first-command behavior of method 1.
Include a normal stop during acceleration and a fresh start after standstill. Confirm that the actual behavior meets the written requirement, not merely that the motor turns in both directions.
Troubleshoot start, reverse and restart problems
| Symptom | Diagnostic question |
|---|---|
| Reverse request appears ignored | Was the selected method waiting for standstill or a valid new sequence? |
| Both requests cause an unexpected result | Which two-wire method is active, and which signal arrived first? |
| Inputs change but the drive stays stopped | Are command source, reference, drive state and permissives correct? |
| Motor runs only while a start button is held | Was a momentary button used with maintained-contact control? |
| Unexpected operation after restart | Were maintained commands retained or reasserted before permission? |
Keep a record of the final PLC output behavior, not only the drive parameters. The installation can behave differently if a PLC update changes retained bits or startup logic while the drive configuration remains unchanged.
For a panel with momentary start buttons, use the companion three-wire control guide. For the speed reference, use analogue input scaling.
Frequently asked questions
Are macros 17 and 18 interchangeable?
No. They differ in handling new direction requests and simultaneous commands. Match the function to the application and verify the timing sequence.
Can I use a spring-return start button?
A two-wire run request is maintained. For a momentary start with a latched run state, consider the supported three-wire configuration.
Will removing a direction request provide a safety stop?
It provides the configured operational stop request. A safety stop requires the machine’s separate designed and validated safety function.
Technical references
Use the document edition matching your installed hardware and firmware. The linked manuals establish the device-specific facts; the worked examples and check sheets are training exercises.