Connecting Siemens MP277 HMI to Omron CQM1 via RS232 Hostlink

Overview

Replacing a legacy desktop HMI with a Siemens SIMATIC MP277 multi-panel while keeping an installed Omron SYSMAC CQM1 PLC requires a properly configured RS232 link running the Omron SYSMAC Way (Hostlink/Multilink) protocol. The Siemens HMI acts as the master on a serial point-to-point or RS422 multi-drop network. WinCC flexible 2008 SP3 and later releases the MP277 for direct SYSMAC Way communication to Omron controllers of the SYSMAC C, SYSMAC CV, SYSMAC CS1, SYSMAC alpha, and CP series, provided the CQM1 CPU is not in the excluded list.

This reference covers the CQM1-CPU45-V (and compatible CQM1-CPU4x variants), the recommended RS232 cable wiring between the MP277 sub-D male and the CQM1 peripheral port, the correct serial parameters (9600 7E2 baseline, 19200 7E2 high speed), the WinCC flexible connection editor configuration, the CQM1 PLC Setup word that must be changed to free Channel 1 from remote ladder transfer, and a verification procedure that confirms end-to-end tag polling before commissioning.

Compatibility Matrix: MP277 to Omron CQM1 CPUs

Siemens AG tested and released Hostlink/Multilink communication for the controllers in the table below. The CQM1 family is partially supported: every CQM1 CPU except the CQM1-CPU11 and CQM1-CPU21 (which lack the full Hostlink frame set) is released.

Identifying the CQM1 CPU Model

Confirm the exact CPU type before wiring. CQM1 modules carry a four-line nameplate on the right-hand side of the unit. For the MP277 ↔ Hostlink path the device must be a CPU4x:

1. Power the rack and open the CQM1 front cover.
2. Read the model code printed above the battery holder. Typical strings: CQM1-CPU45-EV1, CQM1-CPU45-V1, CQM1-CPU44-EV1.
3. Cross-check against the Omron CQM1 Operation Manual (W227-E1) part number list. The -EV1 suffix denotes the enhanced instruction set including floating point, the -V1 suffix denotes a value-line variant with reduced features.
4. If the label reads CPU11 or CPU21 the MP277 cannot establish Hostlink. Replace the CPU or use an Omron CP1L with a serial option board as an alternative.

Hardware: Physical RS232 Connection

The MP277 8-inch and 10-inch variants expose a single 9-pin sub-D male (IF1B) labelled RS422/RS485 on the rear. For Hostlink the port is wired as RS232 using the standard Siemens cable 6XV1440-1K... series or a hand-built crossover conforming to the pinout below.

Connect the shield to ground at one end only to avoid ground-loop noise. Maximum RS232 cable length at 9600 baud is 15 m per the EIA-232-F specification; at 19200 baud reduce to 7.5 m to keep the CQM1 peripheral port receiver within its 3 kΩ input impedance budget.

Protocol: SYSMAC Way Hostlink Frame Structure

Hostlink is a master/slave ASCII protocol on top of RS232 or RS422. The MP277 always originates the request; the CQM1 always replies. Every frame is bracketed by an STX/ETX pair, terminated with FCS (two-hex Frame Check Sum) and CR.

Request:  @ [unit-no] [header-2-chars] [text] FCS CR LF
Reply:    @ [unit-no] [header-2-chars] [text] FCS CR LF
           |   2 BCD   | RH/WR/RL/WL  |  cmd/data   |
FCS calc: XOR of every byte from @ through the last text byte, take low 8 bits, return ASCII hex.

Typical read command used by WinCC flexible to poll IR0 from a unit-00 CQM1:

Master → @00RR00000001 (FCS) CR
Slave  ← @00RR00 (FCS) CR           ← success, data block follows
Master → @00RD00000001 (FCS) CR    ← for DM area, RD command
Slave  ← @00RD1234 (FCS) CR        ← DM0000 = 0x1234

The unit number is BCD 00–31. The default CQM1 unit number is 00. For multidrop with multiple CQM1s, set each CPU to a unique unit number via DM6651 (channel 1 unit number, two BCD digits).

CQM1 Communication Port Setup (Channel 1)

The CQM1 peripheral port (Channel 1) has PLC Setup words DM6650 through DM6653 that control its Hostlink behaviour. Out of the box the port defaults to remote ladder transfer mode, which conflicts with the MP277 polling cycle. Channel 1 must be reconfigured for Hostlink master/slave with the HMI acting as the master.

Procedure using Omron CX-Programmer or a handheld programmer:

1. Connect the programming console to the CQM1 peripheral port (CX-Programmer can use the same port in Hostlink mode if you leave the existing laptop attached to a different port or temporarily disconnect the MP277).
2. Open the PLC Setup and navigate to the Hostlink / Peripheral Port section.
3. Set DM6650 to 0000 (Hostlink master/slave, 9600, 7E2, unit number follows).
4. Set DM6651 to 0000 for a single PLC network, or a unique BCD value (e.g. 0001, 0002) for each additional node in an RS422 multidrop.
5. Set DM6652 and DM6653 to 0000 for no RTS/CTS gating and minimum response delay.
6. Transfer the setup to the PLC. Cycle power to the CQM1 to activate the new mode if CX-Programmer does not send the STUP(237) automatically.
7. Verify with a HyperTerminal / PuTTY session: send @00RR0000000158*\r (where 58 is the FCS for that header) and confirm the CQM1 echoes the IR word 0000.

WinCC flexible 2008 HMI Configuration

After loading the project in WinCC flexible 2008 SP3 (or WinCC Comfort/Professional V11+ for migration), open the Connections editor and add a new connection with the parameters in the table below.

Tag mapping example for reading a process value from DM0100 and a bit from IR010.00:

Tag:    PV_Flowrate
Type:   INT (16-bit, signed)
Address (WinCC flexible): DM 100
Access: cyclic read, 1 s

Tag:    Pump1_Run
Type:   BOOL
Address (WinCC flexible): IR 010.00
Access: cyclic read, 500 ms

Recommended Serial Parameters

The baseline Hostlink profile for CQM1 ↔ MP277 is fixed by the protocol but the optional high-speed variant is permitted when both sides support it. A third-party panel-vendor compatibility reference (Weintek EasyBuilder PLC connection guide for CQM1) confirms the 7E2 / 9600 / 19200 envelope and lists the same RS232 pinout used here:

The protocol mandates 7 data bits, even parity, and 2 stop bits. Any deviation causes every FCS byte to mismatch and the CQM1 will respond with @00IC00 (format error) instead of the requested data.

Multi-Drop Networks (RS422 with Adapters)

Up to four Omron controllers may share one MP277 IF1B port using an RS422 four-wire multidrop topology. Each CQM1 is fitted with a CQM1-CIF11 or NS-AL002 RS232↔RS422 adapter on its peripheral port; the adapter converts TXD/RXD to SDA/SDB/RDA/RDB differential pairs and tri-states when not selected. The MP277 IF1B port must be reconfigured to RS422 mode using the rear-panel DIP switch block (DIP-1 = ON, DIP-2 = OFF for RS422 four-wire) and the WinCC flexible connection must specify the same unit number configured in each PLC's DM6651.

Termination: place a 120 Ω resistor across RDA/RDB at the farthest node only. Each CQM1 unit number must be unique (00–31) and must match the unit number configured in the WinCC flexible connection properties.

Verification Procedure

After physical wiring and project transfer, validate end-to-end communication before handing over to operations:

1. Power the MP277 and the CQM1, then start WinCC flexible Runtime on the panel (or simulate via the WinCC flexible Loader on the engineering PC).
2. Open the Diagnostics → Connection Status view on the MP277. The Omron Hostlink driver should report Connected within one scan cycle.
3. Force a known value into a DM word from CX-Programmer (e.g. write 1234 hex to DM0000). Watch the value appear on the configured MP277 numeric I/O field.
4. Toggle an output bit (e.g. IR100.00) from a button on the HMI. Verify the CQM1 output LED reacts within the configured update time.
5. Disconnect the cable and confirm the MP277 raises an alarm with error code 130002 (communication error, Omron Hostlink). Re-connect and confirm automatic recovery within two scan cycles.
6. Capture a logic-analyser trace of one polling cycle and decode the FCS to confirm both sides agree on the parity and stop bits.

Troubleshooting Matrix

Documentation References

The complete Hostlink driver configuration (Omron chapter) is documented in the Siemens WinCC flexible 2008 Communication Part 2 manual, available through the Siemens Industry Online Support portal under entry ID 18796066. The CQM1 peripheral port pinout and PLC Setup word map are documented in the Omron CQM1 Operation Manual (W227-E1-1) and the CQM1 Programming Manual (W228-E1-1).

A consolidated parameter reference for the CQM1 series, including the 9600 / 19200 baud envelope and RS232 / RS422 / RS485 options, is published by Weintek as a third-party panel compatibility note: OMRON C/CQM1 Series PLC connection guide (Weintek, PDF). Use it as a cross-check on baud and data-bit limits; the protocol behaviour remains defined by Omron and Siemens.