OE Max Controls NX70 series PLC

NX70 Series Programmable Logic Controller: High Performance Small PLC System

In the field of industrial automation, small programmable logic controllers (PLCs) need to provide high processing speed, flexible I/O expansion, rich communication interfaces, and reliable memory backup in a compact size. The OEMax NX70 series controller is designed to meet these requirements, using high-speed ASIC technology with a basic instruction processing time of only 0.2 μ s/step, supporting up to 384 I/O points, and providing multiple dedicated modules (analog, temperature, high-speed counting, motion control, etc.) as well as strong communication protocols. This article will provide a comprehensive and in-depth technical analysis of the series of controllers from the aspects of system configuration, hardware specifications, addressing methods, installation and wiring, programming instruction set, communication protocol, and selection guide.

System characteristics and configuration

The NX70 series PLC adopts a modular chassis structure, which provides multiple models such as 2, 3, 5, 6, 8, 10, and 12 slots. The power module, processor module, and I/O module are installed in left to right order. The system is not expandable (i.e. cannot increase the number of slots by adding a motherboard), but I/O capacity can be flexibly configured by selecting a motherboard with different numbers of slots.

1.1 Processor module

NX70-CP70p1: Program capacity of 9.6k words, 1 RS232/RS485 communication port, basic instructions of 0.2 μ s/step, embedded flash ROM for program backup.

NX70-CP70p2: Program capacity of 20k words, 2 independent communication ports (COM1 and COM2), supports real-time clock (RTC) and PID functions, embedded flash ROM. The COM2 port supports user-defined communication protocols (binary communication) and can be connected to barcode readers, frequency converters, servo drives, etc.

1.2 Power module

NX70-POWER1: AC 110~220V input, output 5V/4.0A and 24V/0.3A.

NX70-POWER2: AC 110~220V input, output 5V/4.5A (no 24V output).

NX70-PWRDC: DC 24V input, output 5V/4.5A.

The power module provides 5V power to all modules through the internal bus of the motherboard. The 24V control power supply (used for input modules and output loads) can be provided by an external commercial power supply or the 24V terminal of POWER1, but parallel use is prohibited.

1.3 I/O module

NX70 supports a wide range of digital and analog modules:

Digital input: 16/32 point DC input (12-24V or 24V), 16 point AC input (110V or 220V).

Digital output: 8/16 point relay output (3A or 1A), 16/32 point transistor output (NPN or PNP), 16 point SSR output.

Combination module: 8 inputs/8 outputs (DC input+relay output), 16 inputs/16 outputs (DC input+transistor output).

Simulation module: 4-channel A/D (voltage/current, 16 bits), 2/4-channel D/A (voltage/current, 14 bits), 4-channel RTD (thermistor), Pt/Ni/Cu）、 4-channel TC (thermocouple, B/R/S/N/K/E/J/T）。

Motion control module: 1/2/4 channel high-speed counter (up to 200 kcps, 32-bit), 4-channel pulse output (up to 100 kHz, with directional control), 4-channel PWM output (30 kHz).

Communication modules: SCU (Serial Communication Unit, RS232/RS485), DeviceNet slave, MW Link network module.

1.4 Programming Tools

Use WinGPC (Windows version) programming software (current version 3. xx) to connect the processor module via RS232/RS485 cable (NX_CBLCPU2/5). Supports programming languages such as ladder diagrams and instruction lists, and allows online editing, forced I/O, timing diagram monitoring, and other functions.

Hardware specifications and installation points

2.1 Environmental and Mechanical Specifications

Working temperature: 0~55 ° C, storage temperature: -25~70 ° C

Humidity: 30~85% RH (without condensation)

Voltage endurance: AC terminal to ground 1500V AC/1 minute, DC terminal to ground 500V AC/1 minute

Insulation resistance: ≥ 100 M Ω (500V DC)

Anti vibration: 10~55 Hz, amplitude 0.75 mm, X/Y/Z for 10 minutes each

Impact resistance: 98 m/s ², 4 times each for X/Y/Z

Installation method: The base plate is fixed inside the control cabinet with M5 screws, and the module is fixed with clamps and screws. During installation, it is necessary to ensure that there is sufficient heat dissipation space around (at least 50 mm up and down), and avoid being too close to high-voltage lines and high-power equipment (≥ 100 mm).

2.2 Power Wiring and Grounding

Use 2 mm ² or thicker twisted pair cables to connect power terminals, and it is recommended to use isolation transformers to reduce noise.

The chassis grounding (FG) terminal must use independent Class III grounding (grounding resistance<100 Ω) to avoid sharing grounding with other devices.

For inductive loads (relay outputs), it is necessary to parallel freewheeling diodes (DC) or impedance capacitance absorption circuits (AC) at both ends of the load to extend the contact life.

2.3 I/O wiring

Terminal type modules (16 points and below) use M3.0 screw terminals, and it is recommended to use flat terminals (Y-shaped or O-shaped) with wire specifications ranging from 0.5 to 1.25 mm ².

The connector type module (32 points) uses two 20 pin MIL connectors (I and II, opposite directions), which can be self crimped using pre fabricated flat cables (NX70_CBLDC or NX70_CBLTR) or pin type components (NX-PIN20).

It is recommended to short-circuit unused channels of the input module (for thermistor inputs, unused channels must be shorted).

The common terminal (COM) of the output module has current limitation, please refer to the specification sheet.

Memory Structure and Addressing

The NX70 adopts a unified bit/word addressing space, with the main areas as follows:

Characteristics of Area Symbol Points/Word Count Address Range

External I/O R 2048 points (128 words) R0.0~R127.15 corresponding to physical input/output modules

Link contact L 1024 points (64 characters) L0.0~L63.15 network shared, can also be used as an internal contact

Internal contact M 2048 points (128 characters) M0.0~M127.15 Power off reset

Maintain contact K 2048 points (128 characters) K0.0~K127.15 power-off hold

Dedicated contact F 256 points (16 characters) F0.0~F15.15 System status (scanning clock, error flag, etc.)

Timer/Counter TC 256 Channel TC0~TC255 Timer (0.01s/0.1s) and counter shared

Data register W 2048 words (p1) or 4096 words (p2) W0~W2047 (p2 extended to W5119), power-off hold, can be accessed by word/double word

Special register SR 512 words SR0~SR511 (or W2560~W3071) CPU status, error codes, RTC, etc

Bit address notation: For example, R0.0 represents the 0th bit of the 0th word (i.e. the first I/O word). Word address notation: W0000 represents the 0th data register. Absolute addresses are used for communication instructions (LDR/STO) and communication protocols, for example, the absolute address of internal contact K127.12 is hexadecimal 1BSC.

I/O addressing is related to slot location: the slot closest to the processor module is assigned the lowest word address. The 16 point module occupies 1 word, and the 32 point module occupies 2 words (input and output are independent). The combination module (such as XY32) occupies 2 word addresses (one word for input and the other for output).

Processor Operation Mode and Diagnosis

RUN mode: Execute user program and update output.

STOP (PROG) mode: Program stops, output is turned off, allowing program modification or download.

Remote mode: Switch RUN/STOP remotely through the communication port.

ERROR mode: Enters when self diagnosis detects hardware or software errors, with output turned off and ALARM LED on.

The monitoring timer defaults to 640 ms, and an error is triggered when it expires. The system provides rich specialized flags (F0. x, F1. x) for detecting ROM/RAM errors, program syntax errors, module type errors, low battery voltage, scan timeouts, etc. For example, F0.0 is the system self-test normal flag, and F0.12 is the monitoring timer error flag.

Overview of Programming Instruction Set

The NX70 supports basic sequential instructions (STR, AND, OR, OUT, SET, RST, DIF, etc.), timer/counter instructions (TIM, TOF, SST, UC, DC, RCT, UDC, SR), compare instructions (CMP, DCMP), arithmetic instructions (ADD, SUB, MUL, DIV, ADC, SBC, etc.), logic instructions (WAND, WOR, WXOR), cyclic shift instructions (RLC, RRC, ROL, ROR, SHL, SHR), word conversion instructions (BCD, BIN, ENCO, DECO, SEG), bit conversion instructions (BSET, BRST, BNOT, BTST) Transfer instructions (MOV, FMOV, BMOV, BFMV, LDR, STO), program control instructions (FOR/NEXT, JMP/LBL, CALL/SBR/RET, INT/RETI), system control instructions (INPR, OUTR, WAT), and communication control instructions (READ, WRITE, RMRD, RMWR, RECV, SEND, etc.).

Among them, the INT instruction can implement fixed cycle interrupts (20 ms~10 s). The LDR/DLDR and STO/DSTO instructions use absolute addresses to access any register, facilitating communication data processing.

Communication Protocol and User Programming

The NX70-CP70p2 provides a complete communication protocol that allows external devices (such as computers, touchscreens) to exchange data with PLCs through RS232/RS485 networks. Communication parameters: Half duplex asynchronous, no parity check, 1 stop bit, baud rate 4800/9600/19200/38400 bps. Adopting a 2-step or 4-step query/response mechanism.

6.1 Communication Frame Structure

Query frame (Q): includes destination address (DA), source address (SA), function code, length, information, and CRC check.

Confirmation frame (QA): A simple confirmation returned by the PLC after receiving Q.

Response Request Frame (RR): An external device sends a request response after receiving QA.

Response frame (R): PLC returns actual data or operation results.

Function code examples: read bit (21H/01H), write bit (22H/02H), read word (23H/03H), write word (24H/04H), etc. Use Q → R directly for 2-step communication, and add QA and RR for 4-step communication to improve reliability.

6.2 CRC Check

CRC-16 (polynomial 0xA001) calculates the coverage of all frame bytes except for the CRC field. The manual provides CRC calculation subroutines for C, Pascal, and BASIC languages.

6.3 User defined Communication

The COM2 port supports user-defined protocols (binary) and can send and receive data in any format through ladder diagram instructions, making it suitable for connecting non-standard devices.

Test run and troubleshooting

The user manual provides the system's testing process: first check the power wiring and module installation, then download the program, place the switch in RUN mode, and observe the status LED. If the RUN LED does not light up, check the program syntax or replace the CPU; If the ERROR LED is on, read the error code in SR017. Common faults include: input unresponsive (external power supply missing or insufficient voltage), output unable to turn off (transistor leakage or relay contact adhesion), module batch failure (motherboard bus error). Regular maintenance: Check the environmental temperature, humidity, terminal tightness, and battery life (approximately 3 years at room temperature) every 6 months.

Selection guide and ordering information

When choosing the NX70 system, the following factors should be considered:

I/O points: Select the number of slots on the motherboard (2-12 slots) based on the actual input/output quantity. Each 16 point module occupies 1 slot, and a 32 point module occupies 1 slot but consumes 2 word addresses.

CPU performance: When large program capacity, dual communication ports, RTC, and PID functions are required, select CPU 70p2; Otherwise, select CPU 70p1.

Power type: When on-site AC 110/220V and 24V auxiliary power supply is required, select POWER1; When only 5V is needed and there is less I/O, choose POWER2; Choose PWRDC for DC 24V power supply.

Special functions: Analog quantity, temperature, high-speed counting, pulse output, network communication, etc. require the selection of dedicated modules.

Programming cable: NX_CBLCPU2 (2m) or NX_CBLCPU1 (5m).