Fifo Almost Full/Empty Flag Offset Range - Xilinx Virtex-5 FPGA User Manual

Chapter 4: Block RAM

FIFO Almost Full/Empty Flag Offset Range

The offset ranges for Almost Empty and Almost Full are listed in
Table 4-18: FIFO Data Depth
Notes:
1. ALMOST_EMPTY_OFFSET and ALMOST_FULL_OFFSET for any design must be less than the total
Table 4-19: FIFO Almost Full/Empty Flag Offset Range
Notes:
1. For limitations under certain conditions, refer to
The Almost Full and Almost Empty offsets are usually set to a small value of less than 10
to provide a warning that the FIFO is about to reach its limits. Since the full capacity of any
FIFO is normally not critical, most applications use the ALMOST_FULL flag not only as a
warning but also as a signal to stop writing.
148
Data Width
FIFO18 FIFO36
x4
x4 x9
x9 x18
x18 x36
x36 x72
FIFO depth.
Data Width
FIFO18 FIFO36 Min
Multirate (Asynchronous) – EN_SYN=FALSE
x4
x4 x9
x9 x18
x18 x36
x36 x72
Synchronous mode – EN_SYN=TRUE
x4
x4 x9
x9 x18
x18 x36
x36 x72
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Block RAM
Memory
8192
4096
2048
1024
512
ALMOST_EMPTY_OFFSET
Standard FWFT
Max Min
5 8187 6
5 4091 6
5 2043 6
5 1019 6
5 507 6
1 8190
1 4094
1 2046
1 1022
1 510
Equation 4-1
Table 4-19.
FIFO Capacity
Standard FWFT
8193 8194
4097 4098
2049 2050
1025 1026
513 514
ALMOST_FULL_OFFSET
(1)
Max Min
8188 4
4092 4
2044 4
1020 4
508 4
1
1
1
1
1
on page 146.
Virtex-5 FPGA User Guide
UG190 (v5.0) June 19, 2009
Max
8187
4091
2043
1019
507
8190
4094
2046
1022
510