The **74AC280** is a high-speed CMOS device designed for parity generation and checking. It is commonly used in digital systems to ensure data integrity during transmission or storage. --- ### 1. General Overview The 74AC280 is a **9-bit Odd/Even Parity Generator/Checker**. It accepts nine bits of input data and provides two outputs indicating whether the number of high levels (logic 1s) at the inputs is even or odd. | Feature | Specification | | :--- | :--- | | **Logic Family** | 74AC (Advanced CMOS) | | **Input Channels** | 9 (A through I) | | **Outputs** | 2 (Sum Even, Sum Odd) | | **Voltage Range** | 2.0V to 6.0V | | **Operating Temp** | -40°C to +85°C | --- ### 2. Functional Pin Description The device typically comes in a 14-pin or 16-pin package (DIP, SOIC, or TSSOP). | Pin Name | Type | Description | | :--- | :--- | :--- | | **A - I** | Input | 9 Data input bits to be checked. | | **$\Sigma$ Even** | Output | High if an **even** number of inputs are High. | | **$\Sigma$ Odd** | Output | High if an **odd** number of inputs are High. | | **Vcc** | Power | Positive supply voltage. | | **GND** | Power | Ground (0V). | --- ### 3. Truth Table Logic The outputs are complementary. If one is High, the other must be Low. | Number of Inputs (A-I) that are HIGH | $\Sigma$ Even Output | $\Sigma$ Odd Output | | :--- | :--- | :--- | | 0, 2, 4, 6, 8 | **HIGH** | LOW | | 1, 3, 5, 7, 9 | LOW | **HIGH** | --- ### 4. Key Advantages of the 'AC' Series The "AC" (Advanced CMOS) designation provides specific electronic benefits over older families (like 74LS or 74HC): * **High Speed:** Propagation delays are typically around 5ns to 8ns. * **High Drive Current:** Capable of sourcing or sinking 24mA, allowing it to drive transmission lines directly. * **Low Power Consumption:** Minimal static power dissipation compared to TTL logic. --- ### 5. Common Applications 1. **Error Detection:** Adding a parity bit to an 8-bit bus (using the 9th input as a fixed ground or control) to detect single-bit errors in memory. 2. **Data Transmission:** Used at both the transmitter (to generate the parity bit) and the receiver (to verify the parity bit). 3. **Cascading:** Multiple 74AC280 units can be linked together to handle 16-bit, 32-bit, or 64-bit words.