CY7C4801/4811/4821
CY7C4831/4841/4851
Document #: 38-06005 Rev. *A
Page 16 of 23
Flag Operation
The CY7C48X1 devices provide four flag pins to indicate the
condition of the FIFO contents. Empty, Full, (PAEA,PAEB), and
(PAFA,PAFB) are synchronous.
Full Flag
The Full Flag (FFA,FFB) will go LOW when the device is full. Write
operations are inhibited whenever (FFA,FFB) is LOW regardless of
the state of (WENA1,WENB1) and (WENA2/LDA,WENB2/LDB).
(FFA,FFB) is synchronized to (WCLKA,WCLKB), i.e., it is exclusively
updated by each rising edge of (WCLKA,WCLKB).
Empty Flag
The Empty Flag (EFA,EFB) will go LOW when the device is empty.
Read operations are inhibited whenever (EFA,EFB) is LOW, regard-
less of the state of (RENA1,RENB1) and (RENA2,RENB2.
(EFA,EFB) is synchronized to (RCLKA,RCLKB), i.e., it is exclusively
Full Flag.
Table 2. Status Flags.
Number of Words in FIFO
FF
PAF
PAE
EF
CY7C4801
CY7C4811
CY7C4821
0
0
0
H
H
L
L
1 to n[26]
1 to n[26]
1 to n[26]
H
H
L
H
(n+1) to (256-(m+1))
(n+1) to (512-(m+1))
(n+1) to (1024
−(m+1))
H
H
H
H
(256
−m)[27] to 255
(512
−m)[27] to 511
(1024
−m)[27] to 1023
H
L
H
H
256
512
1024
L
L
H
H
Number of Words in FIFO
FF
PAF
PAE
EF
CY7C4831
CY7C4841
CY7C4851
0
0
0
H
H
L
L
1 to n[26]
1 to n[26]
1 to n[26]
H
H
L
H
(n+1) to (2048
−(m+1)) (n+1) to (4096 −(m+1)) (n+1) to (8192 −(m+1))
H
H
H
H
(2048
−m)[27] to 2047
(4096
−m)[27] to 4095
(8192
−m)[27] to 8191
H
L
H
H
2048
4096
8192
L
L
H
H
Notes:
26. n =Empty Offset (n=7 default value).
27. m = Full Offset (m=7 default value).
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