The **HT604** is a high-performance, low-cost **Remote Control Decoder** integrated circuit (IC) developed by Holtek Semiconductor. It is primarily used in conjunction with the **HT600** encoder series for wireless communication and automation tasks. --- ### 1. Technical Specifications The HT604 belongs to the 2^12 series of decoders. It is designed to interface with infrared or RF (Radio Frequency) receivers. | Parameter | Specification | | :--- | :--- | | **Operating Voltage** | 2.4V ~ 12V | | **Decoding Series** | 2^12 series | | **Input Pins** | 8 Address pins, 4 Data pins | | **Oscillator** | Built-in RC oscillator (requires an external resistor) | | **Package Types** | 18-pin DIP / 20-pin SOP | | **Standby Current** | 0.1 $\mu$A (at 5V) | --- ### 2. Key Components and Features * **Address Pins (A0 - A7):** These 8 pins allow for $2^8$ (256) unique address combinations. For a successful transmission, the address set on the decoder must exactly match the address set on the transmitter (HT600). * **Data Pins (D8 - D11):** These 4 pins output the data sent from the transmitter. When a valid signal is received, these pins reflect the state of the corresponding switches on the encoder. * **Valid Transmission (VT):** A dedicated pin that goes **HIGH** when the decoder receives a valid sequence of data (usually three consecutive matching words). * **Built-in Noise Filter:** The IC includes circuitry to prevent false triggering caused by electrical noise or interference. --- ### 3. Pinout Configuration A typical 18-pin DIP layout for the HT604 includes: 1. **A0 - A7:** Address inputs. 2. **D8 - D11:** Data outputs. 3. **DIN:** Data input (connects to the RF/IR receiver module). 4. **OSC1 / OSC2:** Connection for the timing resistor ($R_{osc}$). 5. **VT:** Valid Transmission output. 6. **VSS / VDD:** Ground and Power supply. --- ### 4. Application Examples The HT604 is commonly found in "legacy" or "fixed-code" remote systems: * **Burglar Alarms:** Decoding signals from door/window sensors. * **Garage Door Openers:** Simple wireless trigger mechanisms. * **Home Automation:** Controlling lights or fans via a handheld remote. * **Toy Controllers:** Basic RF-controlled vehicles. --- ### 5. Selection Guide (Encoder/Decoder Pairing) To ensure the HT604 works correctly, it must be paired with a compatible encoder. The resistance value of the oscillator ($R_{osc}$) on the decoder must be approximately **4 to 5 times larger** than the resistor used on the encoder (e.g., if the encoder uses 51kΩ, the decoder typically uses 200kΩ-220kΩ).