Set Host Link serial settings on a CS1 or CJ1 PLC

What you need

• The PLC port you will use: a CJ1 CPU's built-in serial port, or a CS1W-SCB21 serial communications board in a CS1.
• CX-Programmer for the PLC Setup; the working CS1 connection described here was configured in version 6.1.
• The panel, with its Omron Host Link driver selected.
• A cable built to the drawing for your exact port: pins 2 and 3 crossed, pin 9 (signal ground) straight through, pins 4 and 5 jumpered at the PLC end.
• One PLC word you control, such as DM100, holding a value you wrote yourself, for the read-back test.

This walk-through covers the Omron Host Link serial case only. The wider choice between a serial protocol and an Ethernet link is set out in connecting a PC HMI to a PLC over a serial protocol or Ethernet.

Check the serial hardware before you touch the settings

On a CS1, the serial board decides whether any setting connects. The reported fix for the revised CS1 Host Link framing is a CS1W-SCB21 board at version 1.2 or higher. Boards at lot number 40613 or lower were reported not to connect even with every setting correct. Read the version marking on the board before you build or configure anything, and check it against Omron's operation manual for the CS1W-SCB@1-V1 serial communications boards, which documents Host Link mode and the board markings.

On a CJ1, the built-in serial port takes the Host Link job directly. The connection that worked used a CJ1H CPU65H whose side label read version 2.0. Open the PLC settings dialog on your CPU and confirm the port offers a Host Link setup with a custom entry before you plan around either case.

Set the PLC side

CS1 with a CS1W-SCB21 board

Open the PLC Setup for the serial board port in CX-Programmer and enter the reported working set:

1. Port setting: user.
2. Serial mode: Hostlink.
3. Serial setting: 7 data bits, 2 stop bits, even parity (7,2,Even).
4. Baud: 38400 bps.
5. CTS control: NO.
6. Protocol setting: 1:N.
7. Hostlink compatible device mode: Mode C.
8. Linkword specification: Continuous I/O refresh.

Transfer the setup to the PLC and restart the CPU; serial settings load at startup.

CJ1 with the built-in port

1. In CX-Programmer, open the settings dialog and go to the Host Link Port setup.
2. Set the setup to Custom.
3. Baud: the same value as the CS1 setup above.
4. Format: 1, which carried 7 data bits, 2 stop bits, even parity (7,2,E) in the working connection.
5. Mode: Host Link.
6. Unit number: 0.

Transfer and restart the CPU the same way.

Set the panel side

Mirror the framing in the panel driver, then add the three Host Link selections:

1. Driver: the PLC's Host Link protocol.
2. Serial framing: the PLC's baud, with 7 data bits, 2 stop bits, parity Even.
3. Transmission: ASCII. Host Link frames travel as ASCII text, and the panel help for Omron drivers states the rule plainly: 7 data bits and 2 stop bits on the PLC side mean ASCII on the panel.
4. Link selector: Multiple, the 1:N choice.
5. Link unit number: 0.

Build the cable to the port's drawing

The reported arrangement is a crossover cable with two Omron-specific details:

Two different cable drawings circulated for this panel-to-PLC pair, so build to the drawing published for your port and check the result pin by pin. Power both units down and pull the cable before probing: continuity from pin 2 at one end to pin 3 at the other, continuity on pin 9 end to end, and the 4 to 5 jumper present at the PLC end only.

Example: what a 7E2 character carries at the set baud

Inputs: the 38400 bps baud on both reported working setups; the framing 7 data bits, 2 stop bits, even parity, set at both ends; 1 start bit per character, which asynchronous serial framing puts in front of every character; and 9600 bps, the common Host Link default, for comparison.

Rule: characters per second equals bits per second divided by bits per character, and bits per character is 1 start plus 7 data plus 1 parity plus 2 stop.

Arithmetic: bits per character = 1 + 7 + 1 + 2 = 11. At 38400 bps, 38400 ÷ 11 = 3490.9, about 3490 characters per second. At the 9600 bps default on the same framing, 9600 ÷ 11 = 872.7, about 872 characters per second. An 8-N-1 port at the same baud would carry 38400 ÷ 10 = 3840 characters per second, but a panel set to 8-N-1 against a 7E2 port decodes none of the stream.

Result: the reported setting moves about 3490 characters per second, roughly four times the 872 characters per second of the 9600 bps default over the same 11-bit character.

Decision: set the faster baud wherever the driver offers it, and keep the 9600 bps default for an older C-series PLC that connects on the standard settings. The number to defend is 11 bits per character: it matches only when both ends run 7 data bits, 2 stop bits, even parity, and any other framing at one end decodes nothing at the other.

Map the panel's Dxxx addresses to DMxxx words

A link that connects but shows wrong values is an address map problem, and the CS and CJ generation changed the address names from the C200 days. The working CJ1 connection mapped the panel's Dxxx references to DMxxx words in the PLC.

1. Pick the PLC word behind each panel object, for example DM100.
2. Enter the panel address that maps to that word, and write the map down object by object.
3. Put a known value in the PLC word, read it on the panel, and compare the word location in CX-Programmer's online view, not only the value.
4. If the value is right but the word is wrong, correct the map before touching serial settings.

When the word is right and the value is still nonsense, the data format is the next suspect; a panel showing nonsense numbers from a PLC BCD analog register is the same class of mismatch one layer deeper.

Check it worked, and where it fails

Write a value you know, for example 1234, into the mapped word and read it on the panel. Then test one write from the panel to a spare word before the panel earns write access to a live control word; the same order of testing is set out in operator panel PLC link setup: test writes before motion. To separate a panel-side fault from a PLC-side one, connect the HMI serial cable to a PLC simulator and run the driver against the simulator first.

Change one layer at a time and repeat the same read test after each change, so a fix at one layer cannot hide a second fault.

Recommendation

Recommendation: On a CS1, read the serial board before anything else: a CS1W-SCB21 at version 1.2 or higher connects, and a board at lot number 40613 or lower is the reason a correct setup still fails, so replace it first. Configure that port as user serial, Hostlink mode, the baud and framing set out above at 1:N, Mode C, continuous I/O refresh. On a CJ1, set the built-in port's Host Link setup to Custom with the same baud, format 1, 7,2,E and unit number 0. Mirror the framing on the panel, set transmission to ASCII, the link selector to Multiple and the unit number to 0, map every Dxxx object to its DMxxx word, and prove the path with a known DM word before the panel writes to anything live.

An HMI panel talks to the PLC; a plant notice screen does a different job. If the same room also needs a board that plays its own notices offline, that is what our factory and plant screens are built for.

Questions