10 exam-style questions with answers and explanations, straight from our 1,030-question bank. Tap an answer to check yourself. When you're ready, take the scored version in the free practice test.
These 10 free C-359 questions are organized by exam domain, so you can see how each part of the Programmable Controller Systems 3 (C-359) blueprint is tested. Reveal the answer and explanation under each question.
Domain 1: distributed I/O via Ethernet
Question 1
A pallet station stops after losing its Ethernet remote-I/O connection. The HMI shows a zero motion command, but a raised pneumatic mechanism retains pressure and can descend. An authorized technician must reach into the pinch point to remove a jam. At this US facility, the machine-specific energy-control procedure requires lockout for this task. What must establish the servicing condition before entry?
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Correct answer: D - Lock out the energy sources, render stored energy safe, and verify isolation under the energy-control procedure.
Domain 2: serial data communications
Question 2
An RS-485 interface has software-controlled driver enable on a two-wire half-duplex bus. Its request reaches the instrument correctly, but the PLC leaves its driver enabled while waiting for the reply. The instrument then attempts to transmit onto the driven pair. The UART transmit-buffer-empty flag can assert before its final character has finished shifting out. What event should release the PLC driver?
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Correct answer: A - The final stop bit of the request has left the UART.
Domain 3: Modbus communication protocol
Question 3
The commissioning record for a Modbus RTU transmitter contains these entries:
Temperature: 16-bit input register, PDU offset 16.
Holding register at offset 16: not implemented.
Request: function 03, starting offset 16, quantity 1.
Reply: valid CRC, function 0x83, exception 0x02.
Which replacement request reads the specified temperature register?
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Correct answer: D - Function 04, starting offset 16, quantity 1.
Question 4
Several instruments respond normally to individual Modbus RTU reads. Their manuals permit a common parameter to be written using function 06 at address 0. After that write, the PLC reports a communication fault because no write response arrives. The application also requires confirmation of each instrument's parameter value. How should this operation be handled?
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Correct answer: B - Allow the broadcast processing interval, then verify each instrument with an individual read.
Domain 4: Statement List programming language
Question 5
In a Siemens S7-300, the following STL begins a new Boolean chain and executes with the master-control region enabled. The comments identify ordinary process-control signals, not safety functions.
A M 0.0 // AutoFeed
AN M 0.1 // ProcessHold
O M 0.2 // ManualFeed
= M 0.3 // FeedRequest
An operator finds that ManualFeed can set FeedRequest while ProcessHold is true. Which expression explains the executed logic?
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Correct answer: B - (AutoFeed AND NOT ProcessHold) OR ManualFeed
Domain 5: programming/interpreting PLC-to-PLC data communications via Ethernet/IP
Question 6
Following a firewall change between two Logix PLCs, explicit tag reads still succeed, but their unicast produced/consumed connection times out. A capture shows that the TCP 44818 session is permitted while cyclic UDP traffic is dropped. The controller addresses and communication path are unchanged. Which narrowly scoped firewall rule is needed for the cyclic exchange?
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Correct answer: C - Permit UDP 2222 between the two controller addresses.
Domain 6: PID instructions
Question 7
Opening a coolant valve lowers tank temperature. During commissioning, a Logix PID is in automatic mode with positive proportional gain, integral and derivative disabled, and .CA = 0. The output is not at a limit. Raising the simulated PV above the fixed setpoint makes the valve command decrease. Scaling and valve direction have been verified. What configuration change restores negative feedback?
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Correct answer: A - Set .CA to 1 for direct action.
Question 8
A flow setpoint is stepped upward while the measured flow remains momentarily constant. The automatic Logix PID has nonzero proportional gain and .DOE = 0, so derivative is taken on PV. Its output is not limited. A technician attributes the immediate output change to a derivative kick from the setpoint step. Which interpretation fits this configuration?
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Correct answer: C - Proportional action can change immediately; the setpoint step itself creates no derivative-on-PV kick.
Domain 7: data arrays
Question 9
A Logix FAL executes once per scan and must update 40 recipe entries, one entry per scan, after a single Start transition. The array bounds and expression are valid. With Mode = INC and the enable rung held true, only the first entry is updated; .DN and .ER remain false. Which change meets the one-entry-per-scan requirement without generating repeated Start pulses?
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Correct answer: C - Select numerical Mode = 1 and continue scanning the instruction.
Domain 9: data conversion instructions
Question 10
A temperature transmitter is configured linearly: 4 mA represents -40 degrees C and 20 mA represents 160 degrees C. The PLC reads a valid 10.4 mA. Its heating inhibit is asserted only when the scaled temperature exceeds 60 degrees C; all other permissives are satisfied. What should the scaling and comparison produce?
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Correct answer: B - 40 degrees C, with the heating inhibit clear.