參數(shù)資料
型號: MACH215-12JC
廠商: LATTICE SEMICONDUCTOR CORP
元件分類: PLD
英文描述: High-Density EE CMOS Programmable Logic
中文描述: EE PLD, 12 ns, PQCC44
封裝: PLASTIC, LCC-44
文件頁數(shù): 18/30頁
文件大?。?/td> 245K
代理商: MACH215-12JC
25
MACH215-12/15/20
fMAX PARAMETERS
The parameter fMAX is the maximum clock rate at which
the device is guaranteed to operate. Because the flexi-
bility inherent in programmable logic devices offers a
choice of clocked flip-flop designs, fMAX is specified for
three types of synchronous designs.
The first type of design is a state machine with feedback
signals sent off-chip. This external feedback could go
back to the device inputs, or to a second device in a
multi-chip state machine. The slowest path defining the
period is the sum of the clock-to-output time and the in-
put setup time for the external signals (tS + tCO). The re-
ciprocal, fMAX, is the maximum frequency with external
feedback or in conjunction with an equivalent speed de-
vice. This fMAX is designated “fMAX external.”
The second type of design is a single-chip state ma-
chine with internal feedback only. In this case, flip-flop
inputs are defined by the device inputs and flip-flop out-
puts. Under these conditions, the period is limited by the
internal delay from the flip-flop outputs through the inter-
nal feedback and logic to the flip-flop inputs. This fMAX is
designated “fMAX internal”. A simple internal counter is a
good example of this type of design; therefore, this pa-
rameter is sometimes called “fCNT.
The third type of design is a simple data path applica-
tion. In this case, input data is presented to the flip-flop
and clocked through; no feedback is employed. Under
these conditions, the period is limited by the sum of the
data setup time and the data hold time (tS + tH). However,
a lower limit for the period of each fMAX type is the mini-
mum clock period (tWH + tWL). Usually, this minimum
clock period determines the period for the third fMAX, des-
ignated “fMAX no feedback.”
For devices with input registers, one additional fMAX pa-
rameter is specified: fMAXIR. Because this involves no
feedback, it is calculated the same way as fMAX no feed-
back. The minimum period will be limited either by the
sum of the setup and hold times (tSIR + tHIR) or the sum of
the clock widths (tWICL + tWICH). The clock widths are nor-
mally the limiting parameters, so that fMAXIR is specified
as 1/(tWICL + tWICH). Note that if both input and output reg-
isters are use in the same path, the overall frequency will
be limited by tICS.
All frequencies except fMAX internal are calculated from
other measured AC parameters. fMAX internal is meas-
ured directly.
tHIR
tSIR
LOGIC
REGISTER
tt
CLK
(SECOND
CHIP)
SCO
t S
fMAX External; 1/(tS + tCO)
LOGIC
REGISTER
CLK
fMAX Internal (fCNT)
LOGIC
REGISTER
t
CLK
S
fMAX No Feedback; 1/(tS + tH) or 1/(tWH + tWL)
16751E-29
LOGIC
REGISTER
CLK
fMAXIR ; 1/(tSIR + tHIR) or 1/(tWICL + tWICH)
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