
MCM69C432
SCM69C432
11
MOTOROLA FAST SRAM
Figure 3. Connections per Second vs Match Cycle Time
MATCH CYCLE TIME AT 50 MHz INPUT CLOCK
0
500
1,000
1,500
2,000
2,500
TYPICAL
WORST CASE
220
320
420
520
620
720
820
920
1020
I
P
TIMING OVERVIEW
CONTROL PORT
The control port of the MCM69C432 is asynchronous.
Data transfers, both read and write, are initiated by the
assertion of the SEL signal. Address values should be valid
and WE should be high, when SEL is asserted to begin
a read cycle. All values (address, WE, and SEL) should be
held until the MCM69C432 asserts DTACK to signal the end
of the read cycle.
Address and data values should be valid and WE should
be low, when SEL is asserted to begin a write cycle. Address,
data, WE, and SEL values should be held until the
MCM69C432 asserts DTACK to signal the end of the write
cycle.
MATCH PORT
The MCM69C432’s match port is synchronous in opera-
tion. When the match width is
initiated by presenting the match data on MQ31 – MQ0 and
asserting the LH/SM signal with the appropriate setup time
relative to the rising edge of the clock. The assertion of the
MC output signifies the completion of the match cycle. If a
32 bits, a match cycle can be
match has been found, the MS output is also asserted. If the
match is a virtual path circuit match in ATM mode, the VPC
output will be asserted with the MS output. Output data, if
any, is enabled by the assertion of the G input.
If the match width is greater than 32 bits, the lower bits are
first latched into the MCM69C432 by the LL input. The match
cycle is then initiated as specified in the previous paragraph.
DEPTH EXPANSION
Multiple CAMs can be cascaded to increase the depth of
the match table. The hardware requirements are very
straightforward, as the following pins on each device are sim-
ply wired in parallel: A2 – A0, DQ15 – DQ0, WE, IRQ,
DTACK, MQ31 – MQ0, K, G, LH/SM, MC, MS, and VPC.
Four CAMs can be easily cascaded. Simulations show that
eight devices can be cascaded if care is taken to minimize
the length of the PC board traces connecting the CAMs.
The buffered–entry mode prevents multiple matching
entries in a single CAM. The check for value instruction
should be used to verify that multiple matching entries will
not result from a potential new entry. If a match is found in
CAM 1, for example, the new value should be placed in CAM 1,
where it will replace the existing entry.