10 / 24 page
CY7C451
CY7C453
CY7C454
Document #: 38-06033 Rev. *A
Page 10 of 24
Notes:
27. The FIFO in this example is assumed to be programmed to its default flag values. Almost Empty is 16 words from Empty; Almost Full is 16 locations from Full.
28. R4 only updates the flag status. It does not affect the count because ENR is HIGH.
29. When making the transition from Almost Empty to Intermediate, the count must increase by two (16 =>18; two enabled writes: W2, W3) before a read
(R4) can update flags to the Less Than Half Full state.
Switching Waveforms (continued)
Read to Almost Empty Timing Diagram with Free-Running Clocks
Read to Almost Empty Timing Diagram with Read Flag
Update
Cycle and
Free-Running Clocks
tSKEW1
tSKEW2
tFD
tFD
tFD
COUNT
17
16
18
16
ENABLED
READ
CKR
ENR
CKW
ENW
E/F
PAFE
HF
17
17
15
ENABLED
WRITE
CKR
CKW
COUNT
17
16
18
16
tSKEW1
tSKEW2
tFD
tFD
tFD
ENR
ENW
PAFE
ENABLED
READ
FLAG
UPDATE
ENABLED
READ
ENABLED
READ
17
17
15
HF
ENABLED
READ
READ
FLAG UPDATE CYCLE
C451-13
E/F
C451-14
HIGH
HIGH
HIGH
HIGH
R1
R2
R3
ENABLED
READ
R4
ENABLED
READ
R5
ENABLED
READ
R6
W1
W2
ENABLED
WRITE
W3
W4
W1
W5
W6
R1
R2
R3
R4
R5
R6
R7
ENABLED
WRITE
W2
ENABLED
WRITE
W3
W1
W4
W5
W6
W7
18 (no change)
[22,25,27]
[22,25,27,28,29]
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