MCM69P618CTQ4 View Datasheet(PDF) - Motorola => Freescale
Part Name
Description
Manufacturer
MCM69P618CTQ4 Datasheet PDF : 12 Pages
| |||
APPLICATION INFORMATION
The MCM69P618C BurstRAM is a high speed synchro-
nous SRAM that is intended for use primarily in secondary or
level two (L2) cache memory applications. L2 caches are
found in a variety of classes of computers — from the desk-
top personal computer to the high–end servers and trans-
action processing machines. For simplicity, the majority of L2
caches today are direct mapped and are single bank imple-
mentations. These caches tend to be designed for bus
speeds in the range of 33 to 66 MHz. At these bus rates,
non–pipelined (flow–through) BurstRAMs can be used since
their access times meet the speed requirements for a mini-
mum–latency, zero–wait state L2 cache interface. Latency is
a measure (time) of “dead” time the memory system exhibits
as a result of a memory request.
For those applications that demand bus operation at great-
er than 66 MHz or multi–bank L2 caches at 66 MHz, the pipe-
lined (register/register) version of the 64K x 18 BurstRAM
(MCM69P618C) allows the user to configure the RAM to
support such designs. Multiple banks of BurstRAMs create
additional bus loading and can cause the system to other-
wise miss its timing requirements. The access time (clock–
to–valid–data) of a pipelined BurstRAM is inherently faster
than a non–pipelined device by a few nanoseconds. This
does not come without cost. The cost is latency — “dead”
time.
Since most L2 caches are tied to the processor bus and
bus speeds continue to increase over time, pipelined (R/R)
BurstRAMs are the best choice in achieving zero–wait state
L2 cache performance. At bus speeds ranging from 66 MHz
to 100 MHz, pipelined BurstRAMs are able to provide fast
clock to valid data times required of these high speed buses.
NON–BURST SYNCHRONOUS OPERATION
Although this BurstRAM has been designed for 68K–,
PowerPC–, 486–, i960–, and Pentium–based systems,
these SRAMs can be used in other high speed L2 cache or
memory applications that do not require the burst address
feature. Most L2 caches designed with a synchronous inter-
face can make use of the MCM69P618C. The burst counter
feature of the BurstRAM can be disabled, and the SRAM can
be configured to act upon a continuous stream of addresses.
See Figure 2.
CONTROL PIN TIE VALUES EXAMPLE (H ≥ VIH, L ≤ VIL)
Non–Burst ADSP ADSC ADV SE1 SE2 LBO
Sync Non–Burst, H
Pipelined SRAM
L
H
L
H
X
NOTE: Although X is specified in the table as a don’t care, the pin
must be tied either high or low.
K
ADDR
A
B
C
D
SE3
E
F
G
H
W
G
DQ
Q(A)
Q(B)
Q(C)
Q(D)
D(E)
D(F)
D(G)
D(H)
READS
WRITES
Figure 2. Example Configuration as Non–Burst Synchronous SRAM
MCM69P618C
10
MOTOROLA FAST SRAM
Share Link: 