
CY7C344
CY7C344B
3
Timing Delays
Timing delays within the CY7C344/CY7C344B may be easily
determined using
Warp2
®,
Warp2
Sim™
,
or
Warp3
® software
or by the model shown in
Figu re 1
. The CY7C344/CY7C344B
has fixed internal delays, allowing the user to determine the
worst case timing delays for any design. For complete timi ng
information, the
Warp3
software provides a timing simulator.
Design Recommendations
Operation of the devices described herein with conditions
above those listed under “Absolute Maximum Ratings” may
c aus e pe rmanen t damage to th e dev ice. This is a st ress rating
only and functional operation of the device at thes e or any other
condi t ions above thos e indica ted in the operat iona l section s of
this datasheet is not implied. Exposure to a bsolute maxi mum
ratings c onditions for e xtended p eriods of time may affect de-
vice reliability. The CY7C344/CY7C344B contains circuitr y t o
protect device pins from high-static voltages or electric fields ;
however, normal precautions should be taken to avoid applying
any voltage higher than maximum rated voltages.
For proper operation, input and output pins must be con-
strained to the range GND ≤ (VIN or VOUT) ≤ VCC. Unused in-
puts must always be tied to an appropriate l ogi c level (either VCC or
GND). Each set of VCC and GND pins must be connected together
directly at the device. Power supply decoupling capacitors of at l east
0.2 µF must be conne cted between VCC and G ND. For th e mos t
effective decoupling, each VCC pin shoul d be separately decoupled.
Timing Considerations
Unless otherwise stated, propagation delays do not include
expanders. When using expanders, add the maximum ex-
pander delay tEXP to the overall delay.
When calculating synchronous frequencies, use tS1 if all inputs
are on the input pins. tS2 shou ld be used if data is ap plied at an I/O
pin. If t S2 is greater than tCO1, 1/tS2 becomes the limiting frequency
in the data-path mode unless 1/(tWH + tWL) is less than 1/tS2.
When expander logic is used in t he data path, add the appro-
priate maximum expander delay, tEXP to tS1. Determin e which of
1/(tWH + tWL), 1/tCO1, or 1/ (tEXP + tS1) is the lowest f requency. The
lowest of these frequenci es is the maximum data-pat h frequency for
the synchronous configuration.
When calculating external asynchronous frequencies, use
tAS1 if all inputs are on dedicated input pins. If any data is appli ed to
an I/O pin , tAS2 must be used as the required set -up time. If (tAS2 +
tAH) is greater tha n tACO1, 1/(tAS2 + tAH) becomes the limiting fre-
quency i n the dat a-path mode unl ess 1/(tAWH + tAWL) is less th an
1/(tAS2 + tAH).
When expander logic is used in t he data path, add the appro-
priate m axi mum expander delay, t EXP to tAS1. Determine which
of 1/(tAWH + tAWL), 1/tACO1, or 1/(tEXP + tAS1) is the lowest frequency .
The lowest of these frequencies is the maximum data-path frequency
for the asynchronous configuration.
The parameter tOH indi cates the system compatibi lity of this device
when driving other synchronous logic with positive input hold times,
which is controlled by the same synchronous cl ock. If tOH is greater
than the m inim um required input hold time o f the subsequent syn-
chronous logic, then the devices are guaranteed to function properly
with a common synchronous clock under worst-case envi ronmental
and supply voltage conditions.
The parameter tAOH indicates the system com patibility of this de-
vice when driving subsequent registered logic with a positive hold
time and using the same clock as the CY7C344/CY7C344B.In gen-
eral , if tAOH is greater than the mi nimum required input hold time of
the subsequent logic (synchronous or asynchronous), then the devic-
es are guaranteed to function properly under worst-case environ-
mental and supply voltage conditions, provided the clock signal
source is the same. This also applies if expander logic is used in the
clock signal p ath of the driving device, but not for the driven device.
This i s due to the expander logic in the second device’ s clock signal
path addi ng an additional delay (tEXP), causing t he output data from
the preceding device to change prior to the arr ival of the clock signal
at the following device’ s register.
Figure 1. CY7C344/CY7C344B Tim ing Model
LOGIC ARRAY
CONTROLDELAY
tLAC
EXPANDER
DELAY
tEXP
CLOCK
DELAY
tIC
tRD
tCOMB
tLATCH
INPUT
DELAY
tIN
REGISTER
OUTPUT
DELAY
tOD
tXZ
tZX
LOGIC ARRAY
DELAY
tLAD
FEEDBACK
DELAY
tFD
OUTPUT
INPUT
C344–7
SYSTEM CLOCK DELAY tICS
tRH
tRSU
tPRE
tCLR
I/O
I/O DELAY
tIO
I/O