OE Max Controls NX70 series PLC

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.