HITACHI EH-150 PLC in depth analysis: characteristics, instructions, and system design

Counter: Supports regular counter (CU), ring counter (RCU), and up/down counter (CTU/CTD). The numbering space of all counters and timers partially overlaps (the first 256 points), so be careful to avoid conflicts when using them.

3.3 Application and operation instructions

Arithmetic operations: Supports four arithmetic operations of binary and BCD codes, logical operations (AND, OR, XOR), and data comparison (=,<>,<,>, etc.).

Data processing: Provides powerful block manipulation instructions such as block transfer (MOV), block copy (COPY), block swap (XCG), and shift/loop shift instructions (SHR, ROR) to facilitate the processing of large amounts of data.

Special function instructions:

PID control (FUN 0-2): In EH-CPU308 (A) and above models, PID operation can be achieved through dedicated instructions without the need for additional hardware modules. It can directly control analog I/O and achieve closed-loop control of process variables such as temperature and flow rate.

Communication command (TRNS0/RECV0): allows user programs to control the universal serial port for custom protocol communication with external devices such as printers, barcode scanners, or frequency converters.

Frequency converter control (FUN 190): specifically designed to control Hitachi SJ300/L300P series frequency converters through RS-485 interface, simplifying the programming of motor control systems.

ASCII/BIN Conversion Instructions: Provides a rich instruction set (such as BINDA, BINHA, ASC, HEX) for converting binary data and various formats of ASCII code, which is crucial for communication with smart instruments, HMI, and other devices.

3.4 Program Control Instructions

Jump and Loop: Program conditional jump is implemented through JMP/CJMP instructions, and program loops are constructed using FOR/NEXT instructions to effectively manage program flow and scanning time.

Subroutine calling: Use CAL instructions to call subroutines defined by SB and RTS, achieving modular programming.

Interrupt program: The INT0-INT3 instructions allow the creation of interrupt programs with periodic execution (cycles of 5ms, 10ms, 20ms, 40ms), used to handle tasks with strict time requirements. The manual specifically states that for a 5ms cycle scan, the program execution time must be strictly controlled to avoid "overload errors" caused by execution timeouts.

Programming and System Operations

4.1 Programming Environment

EH-150 mainly uses Hitachi's dedicated LADDER EDITOR for Windows ®  Software programming. This software supports offline programming, online monitoring, and debugging. When programming, it is necessary to correctly configure the CPU type (choose EH-150 or backward compatible H-302) and memory capacity.

4.2 Scanning cycle and system processing time

EH-150 operates in a periodic scanning mode. A complete scanning cycle includes system processing (such as refreshing timers, communicating with peripheral devices) and user program execution.

Variable system processing time: For enhanced CPUs (EH-CPU * * * A/448/516/548), the system processing time can be adjusted between 1ms and 8ms through a special internal output WRF038. The default value is 2ms, which increases the proportion of user program execution time and can shorten the scanning cycle.

Overload error: When the execution time of a scan exceeds the set overload check time, the system will trigger an overload error. Users can choose whether to continue running during overload through special internal outputs (R7C0, R7C1).

4.3 Program modifications during RUN

EH-150 supports program modification in RUN state, greatly improving the convenience of system debugging and maintenance. When performing "online modification", the CPU will briefly pause (HALT time), complete program modification and verification, and start executing the new program from the next scanning cycle. The modified program will eventually be written into the FLASH backup memory. During this process, the special internal output R7EF will remain in the ON state, reminding users not to cut off the power during this period to prevent program damage.

Safety regulations and fault handling

The manual emphasizes strict safety regulations at the beginning, dividing safety precautions into two levels: "danger" and "caution", accompanied by illustrations.

Installation and wiring:

Environmental requirements: It must be used in the specified environment (temperature, humidity, non corrosive gas).

Grounding requirements: Reliable functional grounding (FE) must be carried out to prevent electric shock and malfunctions.

Emergency stop and interlock: Emphasize that the emergency stop circuit and interlock circuit must be built outside the PLC to ensure equipment safety even if the PLC itself fails. Special warning: External load interlocking should not be achieved by controlling the relay drive power supply of the relay output module.

Battery safety: It is strictly prohibited to reverse, charge, disassemble, heat or short-circuit the battery to prevent explosion or fire.

Fault diagnosis:

The system indicates different levels of errors (severe, moderate, minor, warning) through the combination of on/off/flashing of RUN and ERR LEDs on the CPU module.