54ACT818

8-Bit Diagnostic Register

General Description

The ’ACT818 is a high-speed, general-purpose pipeline reg-

ister with an on-board diagnostic register for performing se-

rial diagnostics and/or writable control store loading.

The D-to-Y path provides an 8-bit parallel data path pipeline

register for normal system operation. The diagnostic register

can load parallel data to or from the pipeline register and can

output data through the D input port (as in WCS loading).

The 8-bit diagnostic register has multiplexer inputs that se-

lect parallel inputs from the Y-port or adjacent bits in the di-

agnostic register to operate as a right-shift-only register. This

register can then participate in a serial loop throughout the

system where normal data, address, status and control reg-

isters are replaced with ’ACT818 diagnostic pipeline regis-

ters. The loop can be used to scan in a complete test routine

starting point (Data, Address, etc.). Then after a specified

number of machine cycles it scans out the results to be in-

spected for the expected results. WCS loading can be ac-

complished using the same technique. An instruction word

can be serially shifted into the shadow register and written

into the WCS RAM by enabling the D output.

Features

n On-line and off-line system diagnostics

n Swaps the contents of diagnostic register and output

register

n Diagnostic register and diagnostic testing

n Cascadable for wide control words as used in

microprogramming

n Edge-triggered D registers

n Outputs source/sink 24 mA

n ’ACT818 has TTL-compatible inputs

n ’ACT818 is functionally- and pin-compatible to AMD

Am29818 and MMI 74S818

n Standard Microcircuit Drawing (SMD) 5962-9160901

Applications

n Register for microprogram control store

n Status register

n Data register

n Instruction register

n Interrupt mask register

n Pipeline register

n General purpose register

n Parallel-serial/serial-parallel converter

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DS100251-3

September 1998

© 1998 National Semiconductor Corporation

DS100251

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