mh2080 Music Semiconductors, Inc., mh2080 Datasheet - Page 15

• Manufacturer Part Number: mh2080
• Description: Hla Packaged Asynchronous Data Recognition And Recall Processor
• Manufacturer: Music Semiconductors, Inc.

Vertical Cascading
A system of any practical depth can be designed by
vertically cascading MH2080s. The scheme uses a daisy
chain to provide system level prioritization as well as
Match, Multiple Match, and Full flags. There are three
daisy chains: Match, Multiple Match, and Full.
When a control state is broadcast that accesses the
highest-priority matching location or Status register, the
daisy chain ensures that only the device that responds is
the one with the highest-priority match in the system. All
other devices will have their DQ31-0 lines and PA:AA bus
outputs held in high-impedance. Therefore, the Match
Flag daisy chain controls access to the system resources
for control states that are conditional on the results of the
previous Compare cycle.
During a Comparison cycle, the Match and Multiple
Match flags will not change until /E goes HIGH during
that cycle. At this time, the daisy chain starts to resolve
system-level prioritization. Once sufficient time has
Rev. 1.1a
Figure 5: Vertically Cascading MH2080’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
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 MH2080 while the
daisy chain is resolving, for example, WR CR, allowing
some degree of pipelining. During a Write cycle, the Full
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 MH2080 architecture supports
external prioritization for cases where the daisy chain
overhead proves unacceptable. Figure 4 shows a system in
which a number of MH2080s are vertically cascaded.
Multi Match
Pull up
(last device set LPC to “0”)
Lowest Priority