74ACT818 Datasheet, PDF (1/6 Pages) Fairchild Semiconductor – 8-Bit Diagnostic Register

July 1988
Revised September 2000
74ACT818
8-Bit Diagnostic Register
General Description
The ACT818 is a high-speed, general-purpose pipeline
register with an on-board diagnostic register for performing
serial diagnostics and/or writable control store loading.
The D-to-Y path provides an 8-bit parallel data path pipe-
line register for normal system operation. The diagnostic
register can load parallel data to or from the pipeline regis-
ter and can output data through the D input port (as in
WCS loading).
The 8-bit diagnostic register has multiplexer inputs that
select parallel inputs from the Y-port or adjacent bits in the
diagnostic 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
registers are replaced with ACT818 diagnostic pipeline reg-
isters. The loop can be used to scan in a complete test rou-
tine starting point (Data, Address, etc.). Then after a
specified number of machine cycles it scans out the results
to be inspected for the expected results. WCS loading can
be accomplished 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
s On-line and off-line system diagnostics
s Swaps the contents of diagnostic register and output
register
s Diagnostic register and diagnostic testing
s Cascadable for wide control words as used in micropro-
gramming
s Edge-triggered D registers
s Outputs source/sink 24 mA
s ACT818 has TTL-compatible inputs
s ACT818 is functionally- and pin-compatible to AMD
Am29818 and MMI 74S818
Applications
• Register for microprogram control store
• Status register
• Data register
• Instruction register
• Interrupt mask register
• Pipeline register
• General purpose register
• Parallel-serial/serial-parallel converter
Ordering Code:
Order Number Order Package
Package Description
74ACT818SPC
N24C
24-Lead Plastic Dual-In-Line Package (PDIP), JEDEC MS-001, 0.300 Wide
Logic Symbol
Connection Diagram
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