11 / 24 page
CY7C451
CY7C453
CY7C454
Document #: 38-06033 Rev. *A
Page 11 of 24
Notes:
30. CKW is clock and CKR is opposite clock.
31. Count = 2,049 indicates Half Full for the CY7C454, count=1,025 indicates Half Full for the CY7C453, and count = 257 indicates Half Full for the CY7C451.
Values for CY7C451 count are shown in brackets.
32. When the FIFO contains 2048[1024,256] words, the rising edge of the next enabled write causes the HF to be true (LOW).
33. The HF write flag update cycle does not affect the count because ENW is HIGH. It only updates HF to HIGH.
34. When making the transition from Half Full to Less Than Half Full, the count must decrease by two (1,025 =>1,023; two enabled reads: R2 and R3) before
a write (W4) can update flags to less than Half Full.
Switching Waveforms (continued)
Write to Half Full Timing Diagram with Free-Running Clocks
COUNT
1024
1025
1023
1025
tSKEW1
tSKEW2
tFD
tFD
tFD
ENABLED
WRITE
ENABLED
WRITE
ENABLED
WRITE
ENABLED
WRITE
ENABLED
READ
ENABLED
READ
1024
1024
1026
C451-15
[256]
[257]
[256]
[255]
[256]
[257]
[258]
Write to Half Full Timing Diagram with Write Flag Update Cycle with Free-Running Clocks
COUNT 1024
1025
1023
1025
tSKEW1
tSKEW2
tFD
tFD
tFD
ENABLED
WRITE
FLAG
UPDATE
ENABLED
WRITE
ENABLED
WRITE
1024
1024
1026
ENABLED
WRITE
ENABLED
READ
ENABLED
READ
WRITE
FLAG UPDATE CYCLE
[256]
[257]
[256]
[255]
[256]
[257]
[258]
CKW
CKR
ENW
ENR
HF
E/F
PAFE
C451-16
CKW
CKR
ENW
ENR
HF
PAFE
E/F
HIGH
HIGH
HIGH
HIGH
W1
W2
W3
W4
W5
W6
R1
R4
R5
R6
R3
R2
W1
W2
W3
W4
W5
W6
W7
R1
R4
R5
R6
R2
R3
R7
1023 (no change)
[255]
[22,30,31,32]
[22,30,31,32,33,34]
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