Cordless barcode scanner to a PLC: base station and serial link

A cordless scanner solves the cable problem at the reading point and creates a new one at the control panel: what exactly does the PLC receive, and through what? The answer is simpler than the radio suggests. The scanner's wireless link ends at its base station; the base then behaves like any wired reader toward the controller, offering a serial port or an Ethernet socket. This guide gives you the decision rule for that host link, the serial timing numbers that size the message and the receive buffer, the framing settings that commission cleanly, and the cases where the cordless pair is the wrong tool. It assumes a compact PLC with a built-in Ethernet port and a slot for a serial communication module — the standard shape of current small controllers.

The decision: choose the host link at the base station

A cordless reader is a pair, not a single device. Reader and base station hold the radio link between them; the base carries the wired host port — RS-232, USB or Ethernet on this class of hardware — and pushes the decoded string to the PLC as plain ASCII. The PLC program never sees the radio and never needs a driver for it, so replacing either half of the pair leaves the controller side untouched.

Choose the wired side on two things: distance, and who consumes the string.

• RS-232 ASCII into a serial communication module for one reader, one PLC, port to port. The EIA-232 guideline is 15 m. No protocol stack, no connection management; the PLC simply reads a terminated line on each scan.
• RS-422/RS-485 ASCII for the same message across a longer or noisier run — the differential pair's guideline reaches 1,200 m at 100 kbit/s.
• Raw TCP/IP when the base can sit on the plant LAN: 100 m per cable segment, extendable with switches, and the same string can feed a second consumer such as a data collector.

One path to avoid: a reader that reaches the PLC only as a fieldbus device, through a PROFINET or EtherNet/IP profile. It integrates tightly on day one and taxes every replacement — a different reader brand means new profile files, new tags, a fresh commissioning cycle. Plain ASCII and raw TCP survive a reader swap unchanged.

The wired-side decision is the same one a wired handheld poses, and Handheld barcode scanner to a PLC without Ethernet: RS232 or USB? works through those port options in detail. The cordless pair only moves where the cable starts: from the scanner's tail to the base station's mount point. More reader-to-controller paths, wired and wireless, sit on the code reading topic page.

Worked example: message time and buffer size

Take a 12-character part number such as A1234567890B with a CR and LF suffix: 14 characters, so 14 × 10 = 140 bits on the wire.

• 9,600 baud: 140 / 9,600 = 14.6 ms
• 19,200 baud: 140 / 19,200 = 7.3 ms
• 38,400 baud: 140 / 38,400 = 3.6 ms
• 115,200 baud: 140 / 115,200 = 1.2 ms

An operator-paced cell triggers two scans per second at most, so a 9,600 baud port carries 2 × 14.6 ms ≈ 2.9% occupancy and could pass about 68 messages per second if anything ever demanded it. In practice the imager's decode time, not the link, sets the pace.

Size the receive buffer to the longest code in the plant, not to the reader's maximum. The 12-character code fits a 32-character buffer with headroom for longer Code 128 layouts; store the bytes and end each message on its terminator, as set out in Storing ASCII barcode strings in PLC memory: bytes, words and clears. Symbol geometry itself — module size, reading angle, how far back the operator can stand — is covered in Code 128 barcode module size, reading angle and reader distance.

The 14.6 ms message also sets the PLC-side rule: at a 5-10 ms scan cycle the string arrives across two or three scans, so end the receive on the terminator character, never on a fixed byte count. A byte-count read can latch half a message caught mid-stream.

RS-232, RS-422 or raw TCP: the numbers that decide

The EIA-232 figure of 15 m belongs to the standard's maximum rate of 20 kbit/s, so a 9,600 or 19,200 baud run to a panel across the aisle meets it comfortably; keep a 115,200 baud port on short shielded cable. The EIA-485 figure assumes termination at both cable ends and needs the RS-485 variant of the serial module, not an adapter hung on an RS-232 port. On the socket path, budget about 10 ms end to end on a switched plant LAN — an estimate, and a conservative one for a handful of switch hops.

Set the pair to plain ASCII

Commission the pair around one message per successful read: decode, string, suffix, send.

• Suffix and preamble. Set a CR suffix and no preamble. A prefix exists for readers feeding several labeled hosts; on a single PLC link it is just garbage in front of a fixed field. The send-on-read behavior, with and without a prefix, is worked through in Barcode scanner capture without a prefix: preamble and serial.
• Port settings. 9,600 baud, 8 data bits, no parity, 1 stop bit, identically on base and PLC module. Any mismatch gives silence or random characters; the diagnosis sequence lives in Garbage characters from a barcode scanner: fix the PLC serial link, and the deeper failure modes are catalogued in this serial communication troubleshooting reference.
• Symbologies. Enable only the code types the plant actually uses. A reader with every symbology on can misdecode a damaged label as a different, shorter symbol.
• Good-read output. Where the base offers a good-read digital output, wire it to a spare PLC input: a scan-event edge independent of the string makes rate counting easy and exposes a stuck reader.
• Back-to-back scans. Two quick scans arrive as two terminated strings. Parse on the terminator and the second scan survives; parse on a timeout and it is lost.

Wire and configure the PLC serial port

Fit the serial communication module to the CPU first. Current compact ranges take one to three of them alongside the built-in Ethernet port, so adding serial does not cost the socket option; count the module positions on your CPU before ordering.

Wire the cable next. RS-232 cares which end is DTE and which is DCE — cross TD and RD when like meets like — and the pinout pitfalls are laid out in RS232 barcode scanner connection to an embedded host. If the base station in hand is USB-only, Barcode scanner interface conversion: USB or RS232 wiring shows the converter route into a serial port.

Then configure the module: baud, parity and stop bits to match the base, receive terminated on CR, and hand each string to the buffer routine. The PLC-side pattern is in Reading a barcode scanner into a PLC CPU module over serial; for the same port fields set end to end on a classic PLC chassis, this barcode scanner serial configuration walkthrough shows the values entered on the controller side.

Two practical points remain. Power: some base stations draw it from the host cable, others need a supply terminal at the mount point, so plan the extra cores. And if the host is a PC-based controller rather than a PLC, the same base and cable work unchanged — connecting a barcode scanner to a PC-hosted controller over serial walks that variant.

If the cell's data path is built on Modbus RTU and you would rather see the last code in registers than parse a stream, that is a different integration: Read a barcode reader into a PLC over Modbus RTU covers it. For one cordless reader feeding one PLC, the plain ASCII stream remains the shorter path.

Ethernet base stations: the socket option

A base station with an Ethernet host port joins the plant network. Give it a static address or a DHCP reservation, then open a TCP connection from the PLC: most current compact CPUs include socket instructions, and the base serves the same ASCII line over that socket. Where the roles reverse — the reader connecting to a listening PLC — the client-versus-listener choice is set out in TCP client or listener: match your network barcode reader to your host.

TCP is a byte stream, not a message bus, so frame the stream with the same CR terminator and send once per successful read; latency lands well inside the 10 ms budget above. The gain is reach and sharing: the string becomes available to anything else on the network, and a second consumer — a data collector, a line historian — can take the same feed. If the base in hand is serial-only but the network is what you have, the converter route is compared in Barcode scanner serial to ethernet converter into plant data tags, and socket-level PLC code with no fieldbus layer at all is in Barcode reader to PLC over raw TCP sockets without EtherNet/IP.

Decision, restated: take the socket path when the run exceeds 15 m, when more than one host needs the string, or when a LAN drop already sits closer to the mount point than a cable route to the control panel.

When a cordless pair is the wrong tool

Three cases call for something else.

Continuous reading on a conveyor has no operator in the loop, which is the whole premise of a handheld. A fixed-mount reader with a trigger sensor is the right shape there; the selection is worked through in High speed conveyor barcode reading: choose the reader and setup.

An operator who never leaves the panel needs no radio and no battery. A USB scanner into the HMI in keyboard mode does the job, and the port decision for that path is in USB barcode scanner on a PLC HMI: HID keyboard mode or serial port — mind the focus behavior described in Keyboard wedge barcode readers and focus in your HMI.

And a workflow that needs choices between scans — pick the part, confirm the bin, key a quantity — needs a computer, not a scanner. Order a terminal for that job:

A terminal runs your application, holds data between reads and talks to a server on its own; a scanner-and-base pair only pushes strings. The workflow design for a tool-crib case, down to the checkout and return logic, is in Barcode tool checkout system: plan a reliable workflow.

Commissioning checklist

Run the pair through this list before it goes to the floor:

• Pair once, then power-cycle both units. A link that re-establishes after a power loss survives a shift; one that needs a menu visit does not.
• Scan a test label and read the raw bytes at the base's host port. Exactly one terminator per message and no preamble bytes mean the send configuration is right.
• Match baud, parity and stop bits on both ends — 9,600, 8N1 as the default. Silence or garbage points at a mismatch before anything else.
• Fire two scans one second apart. Two intact strings confirm the PLC ends each message on the terminator, not on a byte count.
• Range-test the worst position — deepest rack, the operator's natural stance. Ten clean scans in a row, not one lucky hit.
• Wire the good-read output where the base has one, and watch the input bit pulse once per scan.
• Set the docking routine. Nightly dock, a charged spare on the shelf: a flat battery is a silent link, not an alarm the PLC can raise.

When the list holds, freeze the configuration in the reader and note the settings on the panel drawings, so a replaced reader costs minutes of commissioning. The wider picture — scan-event wiring, what the PLC does between messages, retry behavior — is planned in Barcode reader PLC communication: plan a reliable link.

Which parts to order

For the cordless path on a rough floor, the ultra-rugged wireless package is the shape to order:

Decide the package's host side with the table above: a serial module for a panel in the same aisle, the socket path for a networked cell. For the Ethernet story in a single reader, this is the part whose host interface is already network:

Its 1.0 MP global-shutter imager reads the plant's codes, and its wireless connection lands on an Ethernet host interface — the base-plus-socket arrangement described above, one part deep.

If the cell turns out to have no case for a base station at all, a wired USB reader drops the radio and the charging routine entirely:

The handheld code readers category and its finder hold the full range; code reader accessories and its finder cover the host-side boxes and modules. The system configurator assembles reader, link and controller into one order, and open wiring questions go through the contact page.