74ACT818SPC

Overview

The onsemi 74ACT818SPC is an 8-bit diagnostic register housed in a 24-lead Plastic Dual-In-Line (PDIP) package. It operates within a supply voltage range of 4.5V to 5.5V and supports an operating temperature from -40°C to +85°C. The device features edge-triggered D registers with TTL-compatible inputs, capable of sourcing or sinking 24 mA. Propagation delays for the pipeline clock to output range from 2.5 ns to 10.0 ns under standard loading conditions.

Feature Summary

• Integrates an onboard diagnostic register enabling serial diagnostics and writable control store loading alongside normal parallel data pipelining.
• Supports cascading for wide control words used in microprogramming applications.
• Features multiplexer inputs allowing the diagnostic register to operate as a right-shift-only register for system loop testing.

Applications

• Register for microprogram control store
• Status, data, instruction, and interrupt mask registers
• Pipeline and general purpose registers
• Parallel-serial and serial-parallel converters

Procurement Notes

Verify that the specific ordering code matches the required 24-lead PDIP package configuration. Confirm that the component meets the specified ACT logic family requirements for your system design. Ensure compatibility with existing pinouts if replacing legacy components such as the AMD Am29818 or MMI 74S818. Check current availability status as this part originates from historical manufacturing lines.

Selection Notes

Select this component when high-speed 8-bit latching with integrated diagnostic capabilities is required. It is suitable for systems needing simultaneous parallel data transfer and serial shift operations via independent clocks. Consider its functional equivalence to older ACT devices if maintaining backward compatibility with established hardware architectures is necessary.

Part Context

This component belongs to the 74ACT logic family, designed for high-speed digital applications requiring TTL-compatible inputs. The 74ACT818 series specifically addresses needs for complex control logic where internal state monitoring and serial test routines are essential for system maintenance and verification.

Replacement Considerations

Functionally and pin-compatible with AMD Am29818 and MMI 74S818.

FAQ

How does the diagnostic register interact with the pipeline register?

The diagnostic register can load parallel data from the Y-port or adjacent bits to operate as a right-shift register. It can also swap contents with the output register or load the pipeline register from its own output based on the MODE input state.

What determines the data source loaded into the pipeline register?

The MODE control input determines whether the pipeline register loads data from the primary data inputs (D0-D7) or from the output of the diagnostic register during the PCLK transition.