Systems Engineering Associates, Inc.

Systems Electronics Group, Inc.
14989 W. 69th Avenue Arvada, CO 80007
Tel: (303) 421-0484
Fax: (303) 421-8108
Programmable Logic Controller (PLC) Section

The PLC section of the M4500 is a high performance programmable logic controller which incorporates a built-in processor, user program memory, user data memory, RS-232 programming port, interface to the display/keypad, interface to the I/O slots motherboard, and comprehensive diagnostics and internal fault detection.

The scan time of the PLC section is on the order of 0.25 milliseconds per K with scan times as low as 80 microseconds for short programs. Two additional interrupt inputs allow throughputs even less than 80 microseconds. Program memory consists of 32K bytes of battery-backed CMOS RAM. Data memory consists of 8K bytes RAM memory.

The PLC section supports addressing of up to 12 I/O slots. Note that geographical addressing is not used. The slot addresses are specified by dip switches on the I/O board. Addressing for up to 64 bytes is supported at each I/O slot. Memory mapped I/O is incorporated to provide the greatest degree of flexibility in accessing I/O boards. Two 10-30VDC interrupt inputs, two analog inputs, and two analog outputs are incorporated directly into the PLC processor as well.

The program structure of the PLC section is implemented using SYSdev, a windows or DOS based software package that allows the user to create, document, and compile the user logic program as well as directly interface to the M4500 for program download and on-line monitoring. Complete program print-outs including the user program listing, cross reference, and memory map can also be generated.

For more information, download the complete M4500 User's Manual.

Interrupt Inputs

All M4500 modules are equipped with two 10-30 VDC differential interrupt inputs. The interrupts are activated at the "off" to "on" transition of the input. When this occurs, main program execution is suspended and a corresponding user function is called (ufunc00 for IN0, ufunc01 for IN1). At the completion of the user function, program execution resumes at the point in the main program where the interrupt occurred.

These inputs can also be used as standard inputs if desired. In this case, the input would not cause an interrupt but would instead simply be read and mapped to an internal flag for use by the program just like any digital input. Both inputs can be individually enabled or disabled as interrupts as part of the configuration of the module.

The interrupt inputs are true differential inputs which can be wired as either sinking (true low) or sourcing (true high) depending on the device used to drive to input. Individual LED status indication is provided for each input.

Typical applications of the interrupt inputs include general high speed counting (up to 15KHZ) and interfacing to incremental encoders (even quadrature encoders when used in conjunction with the M245).

M4500 Product Line:

General System Features
System Configurations

PLC Section
Interrupt Inputs
Built-in Analog I/O
Diagnostics/Fault Detection

PLS Section
PLS Channel Programming
Advanced PLS Features

Digital I/O Boards
Analog I/O Boards
Communications Boards
Motion Control Boards
Power Supply
SYSdev Program
Development Software

Data Sheets by part number and User's Manuals

For pricing and availability, contact us


Analog I/O

Two analog inputs and two analog outputs are incorporated directly in the M4500.

The analog inputs are 0-5 volt which can be used as 0-20 mA or 0-10 volts as well when external resistors are installed to perform the respective conversion (250 ohm for 0-20 mA, two 10K ohm resistors as a voltage divider for 0-10 volts). The resolution of the analog inputs is 10-bits (0-1023). The inputs also incorporate a high speed conversion time of less than 25 microseconds and are updated once every other main scan.

The analog outputs are 0-10 volt which can be also be used to drive 0-5 volt inputs using a resistor divider network. The resolution of the analog outputs is 8-bits (0-255) and are updated every main scan.

Diagnostic/Fault Detection

The M4500 contains comprehensive fault detection routines which verify the proper operation of the module at all times. In addition, a fault interlock output (24VDC, 500 mA sinking) is incorporated which can be interlocked to the control system for system shut down or annunciation when a fault is detected. Some of the faults detected include:

  • Loss of scan (watchdog timer time-out)
  • Invalid User program (no program loaded)
  • Program memory checksum error
  • User program initiated fault (sfunc09 call)
  • Program execution out of bounds
  • Invalid interrupt

When a fault is detected, program execution is suspended, the "RUN" LED on the M4500 is extinguished, the "FLT" LED is illuminated and the fault interlock output is turned "off". Using SYSdev, the fault can be displayed in the SYSdev fault menu. This menu shows the fault code, a description of the fault, and a suggested corrective action to quickly pin-point the fault and correct it.

In addition to the fault detection, a hardware confidence test is resident in the module to provide a complete test of the internal module hardware. This test is initiated through SYSdev and can be used to verify the M4500 for proper operation.