mh2040 Music Semiconductors, Inc., mh2040 Datasheet - Page 15

• Manufacturer Part Number: mh2040
• Description: Hla Packaged Asynchronous Data Recognition And Recall Processor
• Manufacturer: Music Semiconductors, Inc.

system-level prioritization. Once sufficient time has
elapsed for the daisy chain to be resolved, the PA:AA bus
can be enabled with /OE, and Status Register Read cycles
will access only the highest-priority matching device.
Note that the daisy chain resolves system-level
prioritization combinatorially once initiated by /E going
HIGH. Other cycles that do not affect the daisy chain or
match results can take place in the MH2040 while the
daisy chain is resolving, for example, WR CR, allowing
some degree of pipelining. During a Write cycle, the Full
Full Cascading
The Full flag is set LOW in a particular MH2040 if the /FI
line is LOW, and that device is full. During a Write cycle,
the Full flag will not change until /E goes HIGH during
that cycle. When the /FI line is HIGH, one or more
locations are free in the higher-priority devices; therefore,
when the /FI line is HIGH, whether or not that particular
device is full, its /FF output will remain HIGH. This
method allows the Full Flag daisy chain to recognize
non-contiguous empty locations throughout the entire
MH2040 system.
The daisy chain gives System Full indication. When the
device at the end of the chain has its /FF output LOW, the
entire CAM system is full. The first device in the daisy
Rev. 1.0
HARRP - HLA Packaged Asynchronous Data Recognition-Recall Processors
Figure 5: Vertically Cascading MH2040’s
/DQ
/DQ
/AC
/CS
/AC
/CS
/DQ
/AC
/CS
Match
/MF
/MF
/MF
/MI
/MI
/MI
“1”
/FF
/FF
Full
/FF
/FI
/FI
“0”
/FI
15
/MM
/MM
/MM
flag will not change until /E goes HIGH during that cycle.
There is a small propagation delay per device in the daisy
chain. Alternatively, vertical cascading can be done with
external logic that provides prioritization and select lines
back into each device. The MH2040 architecture supports
external prioritization for cases where the daisy chain
overhead proves unacceptable. Figure 4 shows a system in
which a number of MH2040s are vertically cascaded.
chain has its /FI line tied LOW to ensure data can be
written into the system.
The daisy chain also controls Write at Next Free Address
cycles as well as Read Next Free Address cycles so that
they work globally across the system, and not just locally
in a specific device. Only the device in which the /FI line
is LOW, and which is not full, will respond to the Write
cycle. Therefore, deletions and insertions can be made in
the memory, without the need to keep track of empty
locations.
Match Cascading
The Match flag /MF will be LOW in a particular device
within a vertically cascaded system when its /MI input is
Multi Match
Pull up
(last device set LPC to “0”)
Lowest Priority