An operator interface with a DH-485 driver usually connects straight to the processor's DH-485 channel: build the cable the two manuals show, give each device its own node address, set the maximum node address to the highest one in use, and run 19200 baud at both ends. When a serial port is free, prefer point-to-point DF1 so the interface's polls stay off the token rotation.
An operator interface that speaks DH-485 usually wires straight to the processor's DH-485 channel. When the interface manual's cabling page shows a direct cable, no interface module is needed; the module exists for the other case. Decide the port before anything else: a point-to-point DF1 link on the processor's serial port keeps the screen's polling off the DH-485 token rotation, so take it whenever that port is free. Where DH-485 is the route, the work is three settings: a unique node address per device, a maximum node address at the highest one in use, and a matching baud rate at both ends. The steps below take a small stand from bare connector to live values.
What you need
Two manuals and a bench hour cover it:
- The processor's user manual, open to the serial channel pages. They hold the DH-485 pin table and print the network's device limit.
- The operator interface manual, open to its DH-485 cabling page. That drawing is the authority for the interface end of the cable.
- Shielded twisted-pair cable cut to the run, plus the connectors both drawings call for.
- The PLC programming software, for the channel configuration screens.
- One spare data register, kept for test writes.
The screen choice, its mounting and its update rate are the earlier half of the job; planning a touchscreen operator interface covers them. This page starts where that planning stops: the wire between the two devices.
Read both cable drawings before buying hardware
The interface manual's DH-485 cabling page settles the hardware question in one look. A drawing of a straight cable from the interface port to the processor's DH-485 channel means you build that cable and no module goes in the path. A drawing that places a DH-485/RS-232C interface module between the two means the interface's port speaks RS-232 and the module converts it to the RS-485 wiring DH-485 runs on; follow the drawing. Buying a module first is the common wrong move, because the manual was free to read all along.
Do not judge the processor's jack by its shape. On a 5/03 the DH-485 channel is an 8-pin mini-DIN socket, and people often describe it as RJ-45 style. An RJ-45 plug will not seat in it, and a cable wired to an Ethernet pattern lands the signals on the wrong conductors. Wire from the pin table in the manual, one conductor per listed signal, and land the shield where the two manuals tell you.
Pick the port: DH-485 or point-to-point DF1
If the processor's 9-pin serial port, the DB9 connector, is free, the interface belongs on it. DF1 is point-to-point, so the screen's polls never enter the token rotation, and the rest of the network keeps the speed it had. When that port is already taken, DH-485 is the remaining route, and its cost depends on how busy the network is.
| Situation | Route | Why |
|---|---|---|
| Serial port free | DF1 point-to-point on that port | Screen polls stay outside the token rotation |
| Port taken, training or bench stand | DH-485 direct cable | One added node stretches the rotation little enough to ignore |
| Production network already busy | Free a port for DF1, or move the screen off DH-485 | Every node's polls ride the same token turns |
DH-485 is a token bus. Its limit is 32 devices, the figure the processor user manual prints, and each device holds the token in turn to send its messages before passing it on. Every poll an interface makes rides inside those turns, so each added node and each extra poll lengthens a full rotation, and that shows up as slower screen updates for everyone on the wire. DF1 has no token and no other stations; screen and processor talk only to each other. The same load counting sits behind polling one PLC from several PCs, so decide it the same way: count the talkers first.
Set addresses and baud on both ends
- Set the processor's serial channel to its DH-485 driver in the channel configuration. On a 5/03 the DH-485 channel runs at a fixed 19200 baud; channels that do accept a setting take 1200, 2400, 9600 or 19200.
- Give the processor and the interface different node addresses, both within 0 to 31. Duplicate addresses cause dropouts that come and go, because two stations answer for one token slot.
- Set the maximum node address to the highest address in use, and no higher. The token tours every address up to the setting, so slack in that number is time added to every rotation.
- Fill the same values into the interface's DH-485 driver setup: protocol DH485, the interface's own station address, the maximum station address, and the baud rate. Leave the token hold factor at its default of 1 unless the driver's manual gives a reason to raise it. Field names differ between drivers, but a DH-485 driver asks for exactly these items.
Example: addressing a two-device stand that later takes a laptop
Inputs, with where each comes from:
- Devices: an SLC 5/03 processor and one operator interface, with a programming laptop that joins the same network during training sessions. The device list is the stand's own.
- Limits: 32 devices per DH-485 network, printed in the processor user manual; node addresses 0 to 31, with the maximum station address defaulting to 31 in the interface driver's setup items.
- Rate: 19200 baud, fixed on this processor's DH-485 channel.
Rule in words: every device takes one unique address, and the maximum node address must reach the highest address any device will use, and no further, because the token tours every address below the setting.
Arithmetic: assign the processor address 1 and the interface address 2; the laptop takes the next free address, 3. Highest address in use = 3, so the maximum node address is set to 3. Devices on the wire: 1 + 1 + 1 = 3 of the 32 allowed, so 29 addresses stay spare. With the maximum at 3, one rotation covers addresses 0 through 3, which is 4 stops; a maximum of 31 would make the same rotation cover 32 stops to serve the same 3 devices.
Result: the link comes up with maximum node address 3 and both ends at 19200 baud.
Decision: set the maximum node address to the highest address you will actually use, here 3. Above the highest address in use, the setting only adds empty stops to every rotation. A 33rd device has no address left and does not fit one DH-485 network.
Build the cable and bring the link up
- Power the processor and the interface down.
- Build the cable to the two drawings: one conductor per listed signal, the shield landed where the manuals specify, both connectors seated fully.
- Connect the cable, power up, and load the interface project with its DH-485 driver selected and the processor's node address entered as the target.
- Swap the bench cable for a strain-relieved, labelled one before the stand sees real use, and write the addresses and baud rate on the panel drawing so the next person does not renumber the network.
How to check the link works
- The interface shows live values and raises no communication fault.
- Write a test value from the interface into the spare register and watch the register change in the programming software while online. Change the same register from the programming side and watch the screen follow. A value that moves both ways checks the wiring and the settings end to end.
- Unplug the interface cable and reconnect it. The link should recover without a power cycle. If it does not, recheck the two addresses and the maximum node address first; those are the settings a second pair of hands most often touches.
- Bring the programming node online while the interface runs. When both keep working, the rotation has room for the traffic, which is the point the training stand exists to demonstrate.
A silent link with matched settings usually hides a wiring fault or an address error, the same two faults Modbus RTU master troubleshooting covers on another serial protocol. The triage habit transfers: rate, addresses, then wiring.
Recommendation
Recommendation: Wire the operator interface straight to the DH-485 channel when the manuals show a direct cable and the network is small: unique addresses, maximum node address at the highest one in use, matching baud at both ends. On a production network, put the interface on point-to-point DF1 when the processor's serial port is free, and free that port when it is not, because every screen poll added to a busy token rotation slows every device on the wire.
Keep the cell's notices and line status out of the interface project. A separate shop-floor signage display carries them with offline playback, so a content edit never touches the control link.
Questions
Can I use an Ethernet patch cable on the DH-485 port?
No. On this class of processor the DH-485 channel is an 8-pin mini-DIN socket wired for a serial network, not Ethernet. An RJ-45 plug will not seat, and a cable crimped to an Ethernet pattern puts the wrong signals on the wrong conductors. Build the cable to the pin tables printed in the processor and operator interface manuals, and land the shield where those tables say.
Does the link ever need an interface module?
Only when the operator interface manual's cabling page draws one. A direct-cable drawing means a straight cable is the supported connection, with no module in the path. The module exists for interfaces whose port speaks RS-232: it converts to the RS-485 wiring DH-485 runs on, and it isolates two cabinets that sit on different grounds. Reading that page costs nothing and prevents the usual wasted purchase.
Can DH-485 run slower than 19200 baud?
On a 5/03, no: its DH-485 channel runs at a fixed 19200 baud. Channels that accept a setting take 1200, 2400, 9600 or 19200. A slower rate stretches every message and with it every token turn, so screen updates get slower as the rate drops. If a change is unavoidable, move both ends in the same sitting, or the two devices will never agree.
Planning information, not legal or engineering advice. Rules differ by place: check codes and permits with your local authority and your licensed trades.