Teardown: Inovance H2U-0008ERN Expansion Module

In industrial control systems, the PLC is often referred to as the industrial brain. As a leading enterprise in the domestic industrial automation field, Inovance Technology’s H2U series PLC is widely used in small and medium-sized automation equipment. In this episode,与非网 (EEFocus) tears down an expansion module of the Inovance H2U series PLC—the H2U-0008ERN, a typical digital input/output expansion module used to supplement the I/O count of the main PLC.

Teardown

The H2U-0008ERN expansion module has a relatively simple structure with a snap-fit design, making it easy to remove the internal PCB main board. Inside, there are two PCBs stacked and connected via connectors. One PCB contains the core controller, while the other mainly houses the interfaces and relays.

Let’s first look at the components on the main PCB.

The core chip is an Intel MAX II CPLD, model EPM240T100I5N. This is not a traditional FPGA; it uses an EEPROM-based non-volatile structure, so logic functions are not lost after power-off, and no external configuration memory is required. This makes it particularly suitable for applications where size and power consumption are critical. The EPM240T100I5N contains approximately 240 logic elements and relies on a combination of look-up tables and macrocells to implement small to medium-scale logic control, state machines, interface bridging, and address decoding. Its key advantages are that it runs immediately upon power-up, without the need for the external configuration memory required by SRAM-based FPGAs, and its standby power consumption is extremely low, making it ideal for energy-efficient systems. In terms of applications, CPLDs are often used for protocol processing and interface conversion in communication equipment, logic control in industrial automation, small-scale logic integration in consumer electronics, and as a low-cost alternative to ASIC auxiliary logic. With high stability, low power consumption, and no need for external configuration devices, the CPLD is widely used in scenarios with moderate logic resource requirements, high development cycle demands, and stringent reliability needs.

The ON Semiconductor octal bidirectional bus transceiver, model MC74ACT245DWG, features tri-state outputs. In the module’s circuit, its typical application is data bus isolation and driving. Directly connecting the CPLD’s I/O pins to the system bus may result in insufficient drive capability or signal integrity issues. The MC74ACT245DWG acts as a buffer, enhancing bus drive capability while creating a "protective wall" between the CPLD and external circuits. In the event of module hot-swapping or external circuit abnormalities, the transceiver effectively protects the core CPLD from damage.

The back side of the PCB mainly contains passive components such as resistors and capacitors, as well as LEDs.

Now let’s look at the other interface board.

This side contains signal input processing, signal output processing, and power driving components:

The Nexperia 8-bit parallel-input, serial-output shift register, model 74HC165D. In the expansion module, the 74HC165D is used to expand input channels. Since the CPLD has limited I/O pin resources, cascading multiple 74HC165D devices allows a large number of digital input signals to be read using only a few pins.

The ON Semiconductor 8-bit serial-input, serial-or-parallel-output shift register with tri-state output latches, model MC74HC595ADG. This device performs the opposite function to the Nexperia part. This design allows the CPLD to control a large number of output channels with just a few pins, while the output latches ensure output state stability—even during CPLD data refreshes, the output states do not glitch.

The STMicroelectronics ULN2003DT integrates seven Darlington transistor arrays, each capable of sinking 500 mA, with a withstand voltage of 50 V. It also includes integrated flyback diodes for driving inductive loads. It is responsible for power amplification of the output channels, boosting the weak signals from the CPLD to several hundred milliamperes, enabling it to directly drive the module’s output relays or other external loads.

Now look at the other side of this PCB.

This side is populated with TE Connectivity 24 V power relays, model PCN-124D3MHZ,001B. These are ultra-thin PCB-mount relays serving as the final output switching elements of the expansion module. Driven by the STMicroelectronics ULN2003DT, when the relay coil is energized, the relay contacts close, completing the external load circuit; when the coil is de-energized, the contacts open.

Summary

Through the teardown, it is evident that the hardware architecture of the Inovance Technology H2U-0008ERN expansion module can be summarized as: the backplane bus interface uses the ON Semiconductor MC74ACT245DWG for data exchange with the main PLC; core logic control is handled by the Intel EPM240T100I5N CPLD, responsible for protocol parsing, timing control, and data processing; the input expansion chain uses the Nexperia 74HC165D to convert parallel input signals into serial data for the CPLD; the output expansion chain sees the CPLD serially sending data to the ON Semiconductor MC74HC595ADG, which converts it back to parallel output; the power driver layer uses the STMicroelectronics ULN2003DT to amplify the output signals from the 74HC595 to drive the relays; and the execution layer’s relay contacts directly control external loads. This design fully reflects the typical architecture of industrial control modules: core control + bus isolation + I/O expansion + power driving + execution output, where each layer has a clear role, allowing independent optimization and facilitating fault diagnosis.