This is a library to control the DN24F08, a PLC-style expansion board for the Arduino Nano form factor.
Note: This library was written specifically for the ATmega328p (Nano V3) version due to direct register manipulation.

The board typically comes in several variations: with or without DIN rail mounts, relay or Darlington array outputs (DN23E08 vs DN24F08), and 12V or 24V logic. This library was developed using the 24V, DIN rail mount, Darlington array version.

• RAM Optimization: The library is optimized to reduce RAM usage (e.g., accessing constant arrays via PROGMEM).
• Bare Metal UART: Includes a custom "bare metal" UART library to replace the heavy Arduino Serial class. This allows precise control over RX/TX buffer sizes (the TX buffer was removed entirely to save memory).
• RTOS Ready: The low memory footprint makes this library ideal for use with RTOS implementations on the ATmega328p.

The DN24F08 board.

The board features 8 analog inputs: 4 for current and 4 for voltage.

• Acquisition: 74HC165 (8-bit parallel-load shift register).
• Type: NPN (Sinking). The input must be pulled low (to ground) to register a signal.
• Range: 0-12V or 0-24V (depending on board model).

There are 4 SMD buttons on the board.

The outputs are controlled by a daisy chain of 74HC595D shift registers. The final register in the chain drives a ULN2803 Darlington transistor array (NPN output with built-in flyback diodes).

• Outputs: 8
• Board Names: OUT1 - OUT8
• Range: 0-50V

• Size: 4 Character, 7 Segment.
• Control: Driven by two 74HC595D shift registers (part of the same chain as the digital outputs).

• Chip: SP485.
• Board Names: A+ and B-.
• Pins: Hardwired to the Nano's RX/TX pins.
• Control Pin: D13 is used to toggle Receive/Transmit modes (handled automatically by the library).

Important:

1. DIP Switch: To use RS485, the onboard DIP switch must be in the 485_ON position.
2. Programming: To upload code to the Nano via USB, you must switch the DIP switch to the PRO position.