Overview
The Omron CP1L-series compact PLC supports an optional RS-422A/RS-485 serial channel through the CP1W-CIF01, CP1W-CIF11, or CP1W-CIF12 option boards mounted on the CPU's option board slot. When paired with a Red Lion Graphite, Crimson, or G3-series HMI, the HMI is the master and the CP1L is the slave: the HMI issues polls and the CP1L replies. The link uses Omron's Host Link protocol (C-mode command set), so the PLC side requires no ladder for communication beyond the standard DIP-switch configuration. The HMI does all the tag polling internally through the Omron Host Link driver in Crimson 3.x.
This reference covers the field-proven wiring, DIP-switch, and parameter settings required to bring up a 4-wire RS-485 Host Link between a CP1L and a Red Lion HMI at the default 9600/7/E/2 settings with PLC unit number 00. It also documents the Red Lion DB9 / terminal pin assignments, the corrected transmit/receive mapping, termination practice, and a troubleshooting matrix for the most common field failures.
Prerequisites
- Omron CP1L CPU unit (CP1L-L, CP1L-M, or CP1L-EL/EM family). Reference: CP series CP1L CPU Unit product family page.
- CP1W-CIF01 (RS-422A/485 non-isolated), CP1W-CIF11 (RS-422A/485 optically isolated), or CP1W-CIF12 option board installed in the CP1L option board slot. Reference manual: CP1L CPU Unit Operation Manual (W471).
- Red Lion Graphite, G3, or Crimson-equipped HMI running Crimson 3.x.
- Shielded twisted-pair cable with one overall shield (Belden 3106A or equivalent); two twisted pairs minimum for 4-wire RS-485.
- 120 Ω termination resistor at each physical end of the RS-485 bus.
- Crimson 3.x configured with the "Omron Host Link" (or "Omron C-Series Host Link") serial driver for the COM port connected to the CP1L. Reference: Crimson 3.x Omron communication setup (HMS Networks KB).
Hardware Identification: CP1W-CIF01 vs CP1W-CIF11 vs CP1W-CIF12
All three option boards present the same external 5-pin terminal block (RDA-, RDB+, SDA-, SDB+, FG), but they differ in isolation and ESD/surge robustness. Pick the right board for the plant environment before turning any screwdriver.
| Option board | Standard | Isolation | Max distance | Recommended use |
|---|---|---|---|---|
| CP1W-CIF01 | RS-422A / RS-485 | None | 50 m (RS-485), 500 m (RS-422A) | Short links inside the same cabinet, low-cost. |
| CP1W-CIF11 | RS-422A / RS-485 | 500 V AC optically isolated | 50 m (RS-485), 500 m (RS-422A) | Recommended default for HMI links with different ground potentials. |
| CP1W-CIF12 | RS-422A / RS-485 | 500 V AC optically isolated | 50 m (RS-485), 500 m (RS-422A) | High-noise or long-cable plant floors. |
The CP1W-CIF11 manual documents a six-position DIP switch (SW1) on the rear of the option board. The CP1W-CIF01 uses the same switch layout. Switch functions are documented in W471 Section 8 (Option Board Settings).
DIP Switch Configuration for 4-Wire RS-485
Set the CP1W-CIF01/CIF11 DIP switch as follows before mounting the board on the CP1L. Power down the PLC before changing any DIP switch.
| Switch | Position | Function |
|---|---|---|
| 1 | ON if CP1L is the last device on the bus, OFF otherwise | Termination resistor (120 Ω) insertion across RD pair. |
| 2 | OFF | 4-wire (RS-422A) selection. ON selects 2-wire RS-485. |
| 3 | OFF | 4-wire selection (paired with SW2). |
| 4 | OFF | Not used in Host Link mode. Reserved. |
| 5 | ON | RS (Request to Send) control enabled. Suppresses local echo so the master never sees its own message reflected back. |
| 6 | ON | RS control direction (paired with SW5). |
The CP1L must also be told in software that an option board is present. In CX-Programmer (or Sysmac Studio for the CP1L-EL/EM), open PLC Settings → Option Board and select either RS-422A (4-wire) or RS-485 (2-wire) per the DIP switch position. The PLC will not transmit on the option port until this is set, even if the DIP switches are correct.
Signal Mapping: Omron CP1W-CIF0x to Red Lion RS-485 Port
The CP1W terminal block is a 5-position spring-clamp connector with the following pinout (top to bottom on the board silkscreen):
| CP1W pin | Signal | Direction (from PLC POV) | Meaning |
|---|---|---|---|
| 1 | RDA- | Input | Receive Data A (inverting) |
| 2 | RDB+ | Input | Receive Data B (non-inverting) |
| 3 | SDA- | Output | Send Data A (inverting) |
| 4 | SDB+ | Output | Send Data B (non-inverting) |
| 5 | FG | — | Frame ground / shield drain |
The Red Lion Graphite / G3 / CR3000 serial ports expose a DB9 male connector with the standard Red Lion RS-422/485 pinout. Pin order on the DB9 (looking at the male pins on the HMI):
| DB9 pin | Signal (Red Lion) | Direction (from HMI POV) | Meaning |
|---|---|---|---|
| 1 | TxB | Output | HMI Transmit B (non-inverting) |
| 2 | TxA | Output | HMI Transmit A (inverting) |
| 3 | RxA | Input | HMI Receive A (inverting) |
| 4 | RxB | Input | HMI Receive B (non-inverting) |
| 5 | TxEN | Output | Transmit Enable (asserted by HMI during its Tx window, 2-wire only) |
| 6 | COMM | — | Signal common / isolated ground reference |
| 7 | TxB | Output | Tied to pin 1 internally on Red Lion DB9 |
| 8 | TxA | Output | Tied to pin 2 internally on Red Lion DB9 |
| 9 | — | — | No connection |
The DB9 shield (chassis) is bonded to the HMI chassis ground; do not use it as the COMM/signal reference.
The corrected 4-wire cross-over map for a point-to-point CP1L ↔ Red Lion link is:
| CP1W terminal | → | Red Lion DB9 pin | Twisted pair |
|---|---|---|---|
| RDA- | → | DB9-2 (HMI TxA) | HMI Tx pair |
| RDB+ | → | DB9-1 (HMI TxB) | HMI Tx pair |
| SDA- | → | DB9-3 (HMI RxA) | HMI Rx pair |
| SDB+ | → | DB9-4 (HMI RxB) | HMI Rx pair |
| FG | → | DB9-6 (COMM) | Drain + signal reference |
Cabling Topology and Termination
Use a shielded cable with two twisted pairs (Tx and Rx) and an overall foil + braid shield. Drain the shield to only one end of the link — conventionally at the HMI COMM pin (DB9-6) — and leave the CP1L FG terminal unconnected at the PLC end if the CP1L is the middle of the bus, or connected only if it is the physical far end. Never bond both shield ends; that creates a ground loop that injects 50/60 Hz common-mode noise into the differential pair.
Insert a 120 Ω termination resistor across each pair (between A- and B+) at both physical ends of the bus. The CP1W-CIF01/CIF11/CIF12 provides an internal 120 Ω resistor selectable via DIP SW1. Use it when the CP1L is the last device; otherwise leave SW1 OFF and place an external 120 Ω across the terminals at the physical far end.
Inline topology for a single CP1L and a single Red Lion HMI:
Serial Parameter Configuration (HostLink Defaults)
Omron ships the CP1L with the following Host Link defaults on the option port. Match these exactly on the Red Lion COM port or the master will never see a valid @ response frame.
| Parameter | CP1L default | Red Lion setting |
|---|---|---|
| Baud rate | 9600 bps | 9600 |
| Data bits | 7 | 7 |
| Parity | Even | Even |
| Stop bits | 2 | 2 |
| PLC unit number | 00 | 00 (in driver setup) |
| Protocol | Host Link (C-mode) | Omron Host Link / C-Series |
| Flow control | None (RS control via SW5/6) | None |
If the PLC unit number has been changed in CX-Programmer (under Host Link Settings → Unit Number), update the Red Lion driver configuration to match. Common field values are 00 through 31; address 00 is the broadcast address and should not be used for normal polling.
Configuring the Red Lion HMI in Crimson 3.x
- In the Crimson 3.x project tree, expand Comm and double-click the COM port wired to the CP1L (typically COM1 or COM2).
- Set Port Type to RS-485 4-Wire. If only RS-232 is offered, you are on a port that does not support RS-485; re-wire to an RS-485 capable port or add a Red Lion MCM-RIO module.
- Set baud to
9600, data bits7, parityEven, stop bits2. - Set Driver to Omron Host Link (sometimes labeled Omron C-Series Host Link in older Crimson builds).
- Set PLC Node Address to
00to match the CP1L default unit number. If your CP1L unit number is non-zero, enter it here. - Click Insert Tags and select the CP1L memory areas you need (CIO, W, H, D, E, EM). Host Link supports DM (D) reads and writes, plus CIO bit/word reads and forced-set/reset.
- Save the project and download it to the HMI. The HMI's SD (Send Data) LED on the option board will begin toggling as the master polls the slave.
Reference for the driver behavior: Crimson 3.x Omron communication setup (HMS Networks KB).
Verification and Diagnostics
- Power up the CP1L. The CP1W-CIF11 LED should be green within 2 seconds, indicating the option board is recognized. A red ERR/ALM LED on the CP1L that stays lit indicates an option-board configuration mismatch between the DIP switches and the PLC Settings register; re-check both.
- Watch the SD and RD LEDs on the option board (if fitted) — the SD LED should flash each time the Red Lion sends a poll, and the RD LED should flash when the CP1L replies.
- On the Red Lion HMI, open the Diagnostics → Comm screen. Tx Count should increment monotonically; Rx Count should track within ~100 ms; Error Count should remain at 0. A continuously incrementing Error Count paired with Rx Count near zero indicates wrong polarity or swapped Tx/Rx pairs.
- From a laptop running CX-Programmer, connect to the CP1L via USB and watch PLC Error Log → Comm Option Board. A clean log plus a green RD/SD heartbeat on the option board confirms the link is healthy.
- Force a tag write from the HMI to a known DM word (for example D100 = 1234) and read D100 back from CX-Programmer to verify end-to-end correctness.
Troubleshooting Matrix
| Symptom | Likely root cause | Correction |
|---|---|---|
| HMI Tx increments, HMI Rx = 0 | Tx/Rx pairs swapped, or A/B inverted on one pair | Re-verify RDA-/RDB+ go to HMI TxA/TxB, and SDA-/SDB+ go to HMI RxA/RxB. |
| HMI Rx frames but every byte is FF / checksum error | 2-wire / 4-wire mismatch between DIP switches and PLC Settings | Confirm SW2/SW3 = OFF and PLC Settings → Option Board = RS-422A. |
| Rx frames echoed back exactly as sent | SW5/SW6 set to OFF (RS control disabled) | Set SW5 = ON, SW6 = ON to enable RS control. |
| Intermittent comms, errors climb after 30-60 s | Missing or doubled termination | Place 120 Ω at each physical end only. Remove internal SW1 termination if a mid-bus device. |
| No SD/RD activity at all | Unit number mismatch or protocol driver mismatch | Confirm Crimson driver = "Omron Host Link" and node address matches PLC unit number (00 default). |
| CP1L ERR/ALM red after power-up | Option board not seated, or PLC Settings option board type blank | Reseat the CP1W-CIF11 and re-set the option board type in CX-Programmer. |
| Burst of errors coincident with VFD start | Common-mode noise from unisolated CIF01 | Replace CP1W-CIF01 with CP1W-CIF11 (optically isolated) and re-route cable away from VFD output wiring. |
| HMI displays "No Response" on every poll | Shield grounded at both ends creating ground loop | Lift shield drain at the PLC end; keep drain tied only at the HMI COMM pin. |
Frequently Asked Questions
What is the difference between CP1W-CIF01 and CP1W-CIF11?
Both are RS-422A/RS-485 option boards for the CP1L. The CIF01 is non-isolated; the CIF11 adds 500 V AC optical isolation between the CP1L and the field bus. Use the CIF11 on any link where the HMI and PLC sit on different ground references, or where VFD/servo noise is present.
Can the CP1W-CIF01 run 2-wire and 4-wire simultaneously?
No. The option board is configured for either RS-485 2-wire (half-duplex) or RS-422A 4-wire (full-duplex) by DIP switches SW2 and SW3 together with the PLC Settings register. Pick one mode and wire accordingly.
What are the default serial parameters for Omron Host Link on a CP1L?
9600 bps, 7 data bits, even parity, 2 stop bits, unit number 00. Both the CP1L and the Red Lion Host Link driver must be set to these values; any mismatch yields checksum or framing errors.
Do I need ladder logic in the CP1L for Host Link polling?
No. Host Link is a request/response protocol where the master (Red Lion HMI) sends a command frame containing the memory area and address, and the CP1L replies automatically from its firmware. No communication ladder is required, although you can use the A392/A393 flags or the COMM port instruction if you need to gate polls.
Should I terminate both ends of the RS-485 bus?
Yes. Place a 120 Ω resistor across the differential pair (A- to B+) at each physical end of the bus. On the CP1L, enable the internal termination (DIP SW1) only when the CP1L is the last device; otherwise leave SW1 OFF and add an external 120 Ω at the far end. Never put a third termination in the middle of the bus.
Why does the Red Lion see its own poll echoed back?
DIP switches SW5 and SW6 on the CP1W-CIF01/CIF11 are OFF, so the CP1L's transmitter stays enabled during the receive window and reflects the master's frame. Set SW5 = ON and SW6 = ON to enable RS control and release the bus after each transmission.