Sigmatek control systems built around S-DIAS, C-DIAS and DIAS I/O often stay in service long after commissioning. When a CPU stops booting or an I/O group drops off the bus, maintenance teams need to work out which bus generation they have, read the module LEDs and status numbers correctly, and decide between reprogramming, a refurbished replacement or a component-level repair. This guide covers the CP 112 S-DIAS CPU, the PS 101 power supply module, the CIV 521 VARAN interface and the DDM 165 DIAS module. All technical data comes from Sigmatek's own instruction manuals and product catalog.
Sigmatek control hardware in one picture: VARAN, S-DIAS, C-DIAS, DIAS and LASAL
A Sigmatek control system has three parts: a CPU, a real-time bus and one or more I/O systems. Sigmatek has produced several I/O generations over the years, and a single machine can contain more than one of them.
- VARAN is Sigmatek's Ethernet-based real-time bus. The Sigmatek product catalog states that data is exchanged in hard real time with guaranteed determination at cycle times of up to 100 µs and jitter under 100 ns. VARAN links CPUs, remote I/O heads and DIAS Drive servo amplifiers. On the CP 112, the CIV 521 and the VAC 013 drive interface, each VARAN segment can be up to 100 m long.
- S-DIAS is the DIN-rail I/O system. Its article numbers start with 20-. The CP 112 manual states that a CPU addresses up to 64 S-DIAS modules. The 2026 catalog adds that one supply handles up to 32 modules, or 64 with the PSB 001 power-boost module.
- C-DIAS modules carry article numbers starting with 12-. A remote head such as the CIV 521 powers a decentralized group of up to 8 C-DIAS modules and connects it to the CPU over VARAN.
- DIAS is the oldest bus generation covered here. DIAS I/O modules have article numbers starting with 05-, for example the DDM 165 (05-008-165) and its terminal module DKL 016 (05-024-016). The DDM 165, for example, draws its logic power from the +5 V on the DIAS bus.
- LASAL is the engineering software. CP 112 applications are created with LASAL CLASS 2 and the LASAL SCREEN Editor. The catalog describes LASAL as expanding the IEC 61131-3 standard with object-oriented programming. The CP 112 runs the Sigmatek "Salamander" operating system.
The fastest way to identify the generation is the article number on the module label. A 20- prefix means S-DIAS, 12- means C-DIAS and 05- means DIAS I/O. A newer S-DIAS CPU can reach an older DIAS rack through a CIV 521, which can power and connect both a decentralized C-DIAS group and a decentralized DIAS bus. If you are sourcing Sigmatek parts for a mixed-generation machine, record every article number before you order or ship anything for evaluation.
CP 112 S-DIAS CPU: key data and its dependence on the PS 101
The CP 112 (article 20-004-112, instruction manual Art. 20-004-112-E) is a compact S-DIAS CPU. Its key data from the manual:
| Item | CP 112 data |
|---|---|
| Processor and memory | EDGE2 Technology, 512-kbyte L2 cache, 256-Mbyte DDR3 RAM, 256-kbyte battery-buffered SRAM for remanent data |
| Storage | 4 GB microSD (3D-TLC pSLC), formatted to 1 GB for SLC-like lifetime. Reformatting to the full 4 GB is not allowed. Order no. 12-630-105 |
| Interfaces | 2x Ethernet, 1x VARAN Out (manager), 1x USB-OTG Mini-B, 1x S-DIAS with manager; 1x USB host 2.0 and 1x CAN via the PS 101 |
| Addressable devices | VARAN 65,280 modules; CAN more than 100 participants; S-DIAS 64 |
| Default IP | Ethernet 1 (X4) 10.10.150.1, subnet 255.0.0.0; Ethernet 2 (X3) not configured by default |
| Power | +5 V from the PS 101; S-DIAS bus current typ. 400 mA, max. 450 mA |
| Environment | 0 to +55 °C operating, -20 to +85 °C storage, IP20 |
| Approvals | UL 508 (E247993); UL, cUL, CE, UKCA |
The CP 112 has no power input of its own. Its +5 V comes from the PS 101 power supply module mounted next to it. The PS 101 also provides the CAN port and the USB host port, and it holds the battery that buffers the CPU's SRAM and real-time clock. For this reason the two modules should be diagnosed together. A CPU that will not start may have a supply fault, and a "CAN not working" complaint may come from the supply module rather than the CPU.
Two handling rules from the manual matter during troubleshooting. First, the CP 112 must not be connected or disconnected while voltage is applied. Second, the microSD card must stay formatted to 1 GB.
On lifecycle: the February 2026 Sigmatek product catalog lists the CP 112-2 (article 20-004-112-2), which has an integrated voltage supply that feeds the CPU and the I/O modules. That catalog does not list the plain CP 112 or the PS 101. Documentation for both modules can still be downloaded from Sigmatek's website. Changing to a CP 112-2 is a hardware and project change that needs engineering review. For plants that want to keep the installed design, a refurbished CP 112 is a practical alternative.
Reading CP 112 LEDs and status numbers
Start with the LEDs on the front of the CP 112. They show whether the CPU booted, whether the application is running and whether the networks have link.
| LED | State | Meaning (Art. 20-004-112-E, §7.1) |
|---|---|---|
| Run (green) | On | From power-up until autoexec.lsl is processed, and while the application runs |
| Run (green) | Blinking | Command line interface active, autoexec.lsl being processed, or operating system installation in progress (OS 09.03.054 or later) |
| Run (green) | Off | Error or reset |
| Status (yellow) | Off / application-defined | Off during start, in RUN, and on error or reset; the application can set it |
| Error (red) | Blinking | Error or reset |
| Error (red) | Off | During start and in RUN |
| Run, Status and Error | All dark after power-up, PS 101 "24 V" LED lit permanently | microSD not inserted properly, or the operating system or application on it is faulty |
| VARAN Link / Active | Green / yellow | Link established / data activity on VARAN Out |
| Ethernet Link / Active | Green / yellow | Link established / data activity, per port |
For more detail, connect with LASAL Class and open the status test. The CP 112 manual (chapter 12) lists the status and error numbers below.
Codes and meanings can vary by model, firmware and catalog number, so confirm them against the module's own manual.
| Code | Meaning | What to do |
|---|---|---|
| 00 RUN RAM / 01 RUN ROM | Information: program running | No action needed |
| 02 RUNTIME | Total time of the cyclic objects exceeded the maximum | Optimize the cyclic task, use a faster CPU or adjust the preset |
| 03 POINTER | Invalid program pointer detected before start | Possible causes are missing or defective program memory or a failed buffer battery. Reprogram and replace the battery |
| 04 CHKSUM | Invalid checksum detected before start | Same causes and remedies as 03 POINTER |
| 05 WATCHDOG | Program interrupted by the watchdog | Fix the programming error, or replace the CPU |
| 08 RESET | CPU waiting | Check why the CPU is held in reset; the PS 101 Module Status LED confirms the reset state |
| 09 WD DEFEKT | Watchdog hardware defective | Replace the CPU |
| 10 STOP | CPU stopped | Check in LASAL why the CPU stopped before restarting |
| 17 INT ERROR, 22 MEMORY FULL, 23 NOT LINKED, 24 DIV BY 0 | Application and runtime errors | See the manual's chapter 12 for the specific remedy; usually resolved in the LASAL project |
| 25 DIAS ERROR | Hardware problem accessing a DIAS module | Check the DIAS bus, the CIV 521 head and the addressed module |
| 44 VARAN MANAGER / 45 VARAN ERROR | VARAN manager status (see manual ch. 12) / required VARAN client missing or faulty | Check cables (max. 100 m per segment), client power and the SY LED on remote heads |
| 67 REALTIME RUNTIME / 68 BACKGROUND | Time overruns | Review task load in the application |
| 70 C-DIAS ERROR | C-DIAS error | Check the C-DIAS group and its interface head |
| 72 S-DIAS ERROR | Connection error with an S-DIAS module | Reseat the modules with power removed, then check the module count and supply capacity |
| 75 SRAM ERROR | SRAM error | Check the buffer battery, then the CPU |
| 224-226 LINKING / LINKING ERROR / LINKING DONE | Program linking states | On a linking error, reload the application |
| 240 USV-WAIT | Power disconnected | Check the 24 V supply to the PS 101 |
| 241 REBOOT | Reboot | Information |
| 255 CONNECTION BREAK | Connection break | Check the engineering connection to the CPU |
PS 101 and the buffer battery: Battery Low, lost retentive data and the swap rule
The PS 101 (article 20-003-101, instruction manual Art. 20-003-101-E) accepts +18 to 30 V DC, drawing a maximum of 2.75 A from the +24 V supply. For UL installations the supply must be Class 2 or LVLC. The PS 101 delivers +5 V at max. 1.6 A and +24 V at max. 1.6 A to the S-DIAS bus. It also provides one USB host 2.0 port (480 Mbit/s) and one CAN port. According to the manual, these two ports only work when the PS 101 is used with a CPU module. Operating range is 0 to +55 °C, IP20, with UL 508 (E247993) and UL, cUL, CE and UKCA approvals.
| PS 101 LED | State | Meaning |
|---|---|---|
| Module Status (red) | On | CPU in RESET |
| Battery Low (red) | On | Battery empty |
| CAN active (yellow) | Blinking | Data exchange on CAN |
| DC OK (green) | On | Supply above 18 V |
The buffer battery is a RENATA 3.0 V / 540 mAh lithium cell, Sigmatek order no. 01-690-028. It keeps the SRAM contents and the real-time clock alive for up to three years without supply power. Sigmatek recommends replacing it every year.
Low-battery warnings come in two stages. First, the CPU supervisor reports a weak battery to the control software. If the voltage keeps dropping, the PS 101 Battery Low LED lights. The manual also notes that a battery that reads "good" during operation but "low" after a power cycle should be replaced.
The swap rule: replace the battery only while power is applied. If you pull it with the system de-energized, the SRAM loses its contents. That means losing retentive data such as recipes, counters and calibration values that the application keeps in remanent memory. Before any battery work, back up the retentive data with LASAL, keep the 24 V supply on, and swap quickly. If the CPU then reports 03 POINTER, 04 CHKSUM or 75 SRAM ERROR, reload the application and restore the retentive data before you suspect a hardware fault.
CIV 521 and DDM 165 diagnostics
CIV 521 C-DIAS interface module VARAN
The CIV 521 VARAN interface (article 12-003-521) is a remote head with the following interfaces:
- VARAN In and VARAN Out (RJ45, max. 100 m each)
- Ethernet, tunneled over VARAN (VtE, "VARAN transmits Ethernet")
- RS232 and RS422/RS485 at 9600 to 115000 baud
- TTY 20 mA current loop at 9600 to 57600 baud
- CAN
- A C-DIAS bus and a DIAS bus
It runs on 18 to 30 V DC at max. 1.4 A and supplies up to 1.2 A to the C-DIAS I/O on its bus. An optional Datamover collects the I/O data of the C-DIAS group to reduce VARAN bus load. Hardware versions 1.x to 3.x exist. Operating range is 0 to +50 °C, which is lower than the S-DIAS modules. The module must be mounted standing (vertical) for cooling; any other mounting position requires a fan. If a CIV 521 fails intermittently, check its mounting position and cabinet temperature early in the diagnosis.
| CIV 521 LED | Meaning |
|---|---|
| DC (green) | 24 V and 5 V present |
| R (red) | Module in reset |
| SY (green) | Synchronized with the VARAN manager |
| DA (yellow) | DIAS bus activity |
| Link (green) / Active (yellow) | Per port: Ethernet, VARAN IN, VARAN OUT |
| TX (yellow) / RX (green) | Per serial channel: C1 RS485/422, C2 RS232, C3 TTY, CA CAN |
A configuration limit matters when machines are modified. According to the manual, DIAS modules that require the DIAS interrupt, such as communication modules, must be connected directly to the CPU. Certain C-DIAS modules must also run directly on a C-DIAS CPU and cannot run behind a CIV 521: CSI 021 to 025, CGPS 011 and CBC 021, and from hardware 3.x also CME 021, CME 221, CNC 115, CNC 305, (T)CCA 021 and CDI 162. A module that cannot be reached because of this rule is a configuration issue, not a hardware defect.
DDM 165 DIAS digital conversion module
The DDM 165 DIAS module (article 05-008-165) is a 16-channel digital output module with read-back. It is not an input module. Its outputs are +24 V, positive switching, short-circuit protected and rated 2 A continuous per channel. Total current is limited to 6 A per group of four channels and 24 A for all 16 channels at 100 % duty.
Because the output states can be read back, channels can also be used as inputs. In input mode the nominal level is +24 V (30 V max.), Low is below +8 V, High is above +14 V, the input draws 7 mA at 24 V and the input delay is 5 ms. Each group of four channels has its own 18 to 30 V DC supply, and the module logic takes typ. 30 mA (max. 50 mA) from the DIAS bus +5 V.
The DDM 165 needs the DKL 016 terminal module, a 17-pole 3-row spring terminal. On the DIAS bus it has module ID 16#63, and the software macro is DDM165.fub. It is rated for 0 to +60 °C with UL (E247993).
Diagnostics on the DDM 165:
- LEDs: one yellow LED per output. If the +24 V supply to a group is removed, the LEDs show the actual output state, not what the CPU commanded.
- Read-back word at 16#00: the actual state of each output.
- Error byte at 16#04: one bit per output pair (1+2 through 15+16). A set bit reports no-load (open-load detection in the 20 to 300 mA range), a short circuit, or overheating/overload.
- Group rule: within one supply group, such as +24V/1, all four channels must be used as inputs or all four as outputs. Mixing inputs and outputs in a group is not allowed. If a DDM 165 reads strange values after a field rewire, check this rule first.
A note on open-load detection: very small loads may draw too little current for the module to register them. If a pair reports no-load while the load is connected and working, check the load current against the detection range before you suspect the module.
When the module needs repair, not reprogramming
Most status numbers point back to the application, the battery or the wiring. Some patterns, however, point inside the hardware. General signs a PLC is failing apply to Sigmatek as well. These are the specific cases in which, based on the manual's remedies, a Sigmatek module should go for evaluation:
- 09 WD DEFEKT. The manual says the watchdog hardware is defective and the remedy is to replace the CPU. Software changes will not fix it.
- 05 WATCHDOG that returns after the program is fixed. The manual lists two remedies: fix the programming error or replace the CPU. If the error comes back after the code has been corrected and reloaded, or appears with a known-good project, the CPU is the likely cause.
- 25 DIAS ERROR with good cabling and a correct configuration. The manual calls it a "hardware problem" accessing a DIAS module. Swap the modules one at a time, including the CIV 521 head, to find the faulty one.
- 04 CHKSUM that returns with a new battery. Once the battery is replaced and the application reloaded, a checksum error that keeps returning points to defective program memory rather than lost backup voltage.
- Dark Run, Status and Error LEDs with a known-good microSD. The manual links this symptom to a missing or faulty card. If a card that boots another CP 112 does not boot this one, the CPU or its supply needs attention.
- DDM 165 short-circuit reports with the load disconnected. If the error byte still reports a short on a pair with the field wiring removed at the DKL 016, the fault is inside the module's output stage.
- CIV 521 that stays in reset (R LED) or will not show SY on good VARAN cables, with correct 24 V and the DC LED lit.
In each of these cases, reloading the project costs downtime without solving the problem. Hand the unit over to a PLC repair service that can test it, or install a tested replacement.
Refurbished modules or repair: keeping a Sigmatek machine running
Flexa Systems is an independent US supplier of new and refurbished industrial automation parts and component-level repair. It is not affiliated with Sigmatek. For the modules in this guide, stock is as follows:
- CP 112 (20-004-112): available refurbished. Repair is quoted on request.
- PS 101 (20-003-101): available refurbished. Repair is quoted on request.
- CIV 521 (12-003-521): available refurbished, and also available as a repair service.
- DDM 165: repair service only.
- Sigmatek control cabinet PC (01-310-325-K): repair service only. See Sigmatek 01-310-325-K control cabinet PC repair and our industrial PC repair page.
- Other Sigmatek modules: repair and quote on request.
Where a refurbished unit is available, buying one and repairing the failed unit are equally valid options, and the choice depends on the downtime situation.
A refurbished CP 112, PS 101 or CIV 521 gets the machine running quickly. You can then send the failed module in for repair and keep it as a tested spare. Repair keeps your existing hardware and its hardware revision, which matters for CIV 521 units because some C-DIAS restrictions depend on whether the head is hardware 1.x, 2.x or 3.x. It is also the route for parts not offered refurbished, such as the DDM 165. Browse PLC modules in stock for refurbished units. Repaired and refurbished units are backed by a 2-year warranty.
For a smooth swap, back up the LASAL project and retentive data first. Move the microSD card from the old CPU to the replacement, power down before removing or inserting S-DIAS modules, and fit a fresh buffer battery with power applied. If the same machine also uses DIAS Drive amplifiers on VARAN, see our article on Sigmatek DIAS Drive servo repair. For line-down situations, our rush repair service puts your unit at the front of the queue. To get pricing and availability, request a quote with the article number, hardware version and observed fault, or call Flexa Systems at (254) 254-0005.
Frequently asked questions
Can a CP 112 run without a PS 101?
No. The CP 112 receives its +5 V from the PS 101, and its CAN port and USB host port are physically on the PS 101, which also holds the buffer battery for the SRAM and real-time clock. The current Sigmatek catalog lists the CP 112-2, which has an integrated supply. Changing to it is a design change that needs engineering review.
Why did my machine lose recipes after a battery change?
The PS 101 battery buffers the CPU's SRAM and real-time clock. The CP 112 manual requires battery exchange with power applied. Removing the battery with the system de-energized erases the retentive data. Restore it from a LASAL backup. If the CPU shows 04 CHKSUM or 03 POINTER afterwards, reload the application before suspecting hardware.
Is the DDM 165 an input module or an output module?
Sigmatek's manual describes the DDM 165 as a 16-channel digital output module, +24 V and 2 A per channel, positive switching. Because outputs can be read back, channels can also serve as inputs, but all four channels in one supply group must be either inputs or outputs. Mixing within a group is not allowed.
What does 09 WD DEFEKT mean on a CP 112?
The CP 112 manual defines 09 WD DEFEKT as defective watchdog hardware, and the remedy it gives is to replace the CPU. Reprogramming will not clear it. Flexa Systems offers refurbished CP 112 units and quotes CP 112 repair on request, with repaired and refurbished units covered by a 2-year warranty.
Why does the CIV 521 not show the SY LED?
SY lights green when the CIV 521 is synchronized with the VARAN manager. If it stays dark, check that the DC LED shows 24 V and 5 V present and that the R LED is not indicating reset. Also check the VARAN cables, which are limited to 100 m per segment, and confirm the module is mounted vertically or has fan cooling.
