C-842 DC Motor Controller PC Board for Closed-Loop Servo Motors

  • ISA Bus Compatible Simultaneous
  • Control of up to 4 Closed-Loop Servo Motors
  • Fast 32 bit Digital PID V-ff Servo Loop
  • On-Board Linear Power Amplifiers (12 bit) and PWM Outputs
  • Trapezoidal-Curve, S-Curve & Velocity Contouring
  • LabView Drivers, Libraries for C, PASCAL, etc.
  • Programming Tools for Win 95, NT, 3.1 and DOS
  • Hardware Interrupts for Process Control
  • High Level Command Language Interface
  • 16 I/O Lines for Flexible Automation
  • 12 TTL Inputs for Limit & Origin Switches
  • Electronic Gearing
  • Programmable Torque Limit
  • Motor Brake Control Output (Versions C-842.xxB)

The C-842 PC plug-in programmable servo motor controller board is the optimal solution for applications where a multi-axis precision motion stage is to be computer controlled by a PC. Integrated low noise, linear amplifiers allow operation of compact micropositioning stages with motor / gear box drives without additional external amplifiers, reducing costs and simplifying the set-up.

The C-842 is equipped with a fast DSP (Digital Signal Processor) providing high performance closed-loop PID motion control with many options of trajectory generation and filter setting. Position, velocity, acceleration and several other motion parameters can be programmed individually for each axis on-the-fly. The C-842 can be installed in 16-bit ISA PC slots.

Additional high-performance advanced motion controllers and drivers, including EtherCat based industrial motion controllers can be found here:

Any quadrature TTL incremental encoder can be used for position feedback (linear scales and rotary encoders, interferometers). Eight TTL inputs and eight TTL outputs are available for flexible automation (trigger functions etc.).

More information on motion control software tools from PI

The C-842 offers full access to the internal processor functions via the I/O address space. Programmers can use hex commands and 32-bit parameters for very fast communication (3000 data/sec). The motor controller also comes with a variety of software tools such as LabView drivers, libraries in C, PASCAL and BASIC and a DOS program for instant, easy operation without low-level programming. Windows programming is supported by 32 bit and 16 bit DLLs.

Learn more about advanced motion control algorithms and motion systems for PCB board manufacturing

 DC Servo Motor Controller PC Board, 2 Axis
C-842.40 DC Servo Motor Controller PC Board, 4 Axis
C-842.20B DC Servo Motor Controller PC Board, 2 Axis, Brake Output
C-842.40B DC Servo Motor Controller PC Board, 4 Axis, Brake Output



PC Bus compatible DC-Servo Motor Controller


4 (C-842.40); 2 (C-842.20)

Servo characteristics

32 bit programmable PID V-ff filter, 100 m s/ enabled axis, parameter changes on-the-fly

Profile modes

trapezoidal, S-curve, velocity contouring, electronic gearing

Output power / resolution

analog H-bridge ± 12 V, 5 Watts/channel, 12 bit D/A converters,
optional output for PWM drivers (10 bit, 24 kHz)

Current limitation

1 A peak (short circuit proof)

Encoder input

AB (quadrature) TTL signals (single ended or RS-422 differential mode), max. 106 counts / sec

Stall detection

servo off, triggered by programmable position error

Limit switches

8 TTL (pull-up/ pull-down, programmable)

Origin switches

4 TTL (pull-up/ pull-down, programmable), real time position capture

I/O ports

8 TTL inputs, 8 TTL outputs (pull-up)

Motor connectors

4 x 15 pin (f) D-Sub (2 on board, 2 on bracket holder)

Interface / Communication

PC ISA bus, I/O mapped, interrupt break point capability

Command set

> 100 high level commands

Host software &
programming Tools

DOS, Windows 95ä DOS window: QMove operating program, Joystick Tools.
LabViewä drivers (Windows 95ä)
Libraries for C, Pascal, BASIC, Delphi
16 and 32 bit DLLs for Windows 3.1 & 95 ä,
device driver and DLL for Windows NTä 


Software for C-842 DC Motor Controllers

The C-842 is based on the MC1401 PMD chip set to generate motion trajectory and digital servo loop filtering. This sophisticated DSP system supports more than 100 commands for trajectory control, servo filtering, breakpoint handling, position referencing and many other tasks.

At the hardware level, communication is via hexadecimal commands, transferred byte by byte from the operating software to the PC I/O port. The C-842 documentation comes with the full DSP command set to allow hardware level programmers direct programming of all registers. For users who don’t want to deal with hexadecimal commands, a variety of software tools is provided with the C-842 controller.

Software libraries for all major programming languages provide a simple user interface which only requires specification of board address, motor channel and the motion command with the optional parameter.


C-842.TO Software Tools Distribution Disk (included)

QMove Interactive Operating ProgramQMove is a general purpose operating program providing a set of mnemonic short form commands. An online display of all motor positions and major motion control parameters reflects the system status.

QMove allows single command execution and macro command file handling for multi axis motion. Complex positioning procedures can be programmed using stackable macro command loops.

QMove runs under DOS but can also be used without restrictions as a DOS task under Windows 3.1 or Win95. It comes free on the C-842 Tools distribution disk.

QLink is an interface program that converts ISA bus PCs (286 and later, keyboard and monitor not required) running DOS into stand-alone motor controllers with RS-232 interface. The C-842 has to be installed in the host PC and QLink is executed. The PC now behaves like a stand-alone motor controller and can be controlled via the RS-232 interface. Ideal for users who want to operate the C-842 remotely or by a computer without ISA bus.

QLink runs under DOS but can also be used without restrictions as a DOS task under Windows 3.1 or Win95. It comes free on the C-842 Tools distribution disk.

QHEX is an interface program that converts ISA bus PCs running DOS into stand-alone multi axis DC motor controllers. Up to four C-842 with a total of 16 axes can be installed and remotely operated via the RS-232 interface. All QFL short form commands are available with extended axis specifier referring to axis numbers 1 through 16.

Programming Tools for C-842
Programming Tools for all major programming languages are available and provide convenient access to the basic functionality of the C-842 board. Exceeding the generic commands of the processor firmware, the libraries offer many features like high level command (mnemonic code) communication, command sequencing (macro commands), etc. Also byte-based low level commands can be used for fast transfer up to 3000 communication cycles/s. See table for availability.


Operating System

Development Environment

Library / Tool


Borland CTM
Borland Turbo PascalTM
Borland Pascal 7TM
MS QuickBasic 4.5TM

QFLMC library
QFLC library
QFL library
QFL library
QQB library

Windows 3.1TM

Borland Pascal 7TM
Borland Delphi 1.0TM (16 bit)
MS Visual C++TM
MS Visual BasicTM (16 bit)
National LabView 3.1TM

C842VI Library *

Windows 95TM

Borland Delphi 2.0TM (32 bit)
MS Visual C++TM
MS Visual BasicTM (32 bit)
National LabView 4.1TM

C842VI Library *

Windows NTTM

Borland Delphi 2.0TM (32 bit)
MS Visual C++TM
MS Visual BasicTM (32 bit)

NT Device Driver + 842NT.DLL


* Note: LabView drivers are not included and can be ordered free of charge. Order number is C-842.LV.

QStick Joystick Package

A joystick is a convenient tool to manually control XY positioning stages. C-842.JS includes the C-819.10 analog joystick, a game-port adapter and a software package for operation of up to 8 axes (two C-842.40 boards) with one joystick via the PC game-port adapter. The joystick is initialized and calibrated automatically after the software is started. Options such as fine speed control, command line editor and limit switch recovery round out the software.

The QStick software runs under DOS but can also be used without restrictions as a DOS task under Windows 3.1 or Win95TM.

This is a legacy product that may have limited availability or may have been replaced. Ask a PI engineer for an equivalent new model

Precision Motion Controller Overview


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