IDT72511/IDT72521
BIDIRECTIONAL FIRST-IN FIRST-OUT MEMORY
MILITARY AND COMMERCIAL TEMPERATURE RANGES
CONFIGURATION REGISTER FORMATS
15
10
9
0
Config. Reg. 0
X
15
X
X
X
X
X
10
9
A→B FIFO Almost Empty Flag Offset
0
Config. Reg. 1
X
15
X
X
X
X
X
10
9
A→B FIFO Almost Full Flag Offset
0
Config. Reg. 2
X
15
X
X
X
X
X
10
9
B→A FIFO Almost Empty Flag Offset
0
Config. Reg. 3
X
15
X
X
X
12
X
11
X
8
B→A FIFO Almost Full Flag Offset
7
4
3
0
Config. Reg. 4
Flag D Pin Assignment
15
Flag C Pin Assignment
Flag B Pin Assignment
Flag A Pin Assignment
0
Config. Reg. 5
15
General Control
0
Config. Reg. 6
15
I/O Data
0
Config. Reg. 7
NOTE:
1. Bit 9 of Configuration Registers 0-3 must be set to 0 on the IDT72511.
I/O Direction Control
2668 drw 02
2668 tbl 10
Table 8. The BiFIFO Configuration Register Formats
EXTERNAL FLAG ASSIGNMENT CODES
Programmable Flags
The IDT BiFIFO has eight internal flags. Associated with
each FIFO memory array are four internal flags, Empty,
Almost-Empty, Almost-Full and Full, for the total of eight
internal flags. The Almost-Empty and Almost-Full offsets can
be set to any depth through the Configuration Registers 0-3
(see Table 8). The flags are asserted at the depths shown in
Table 11. After a hardware reset or a software Reset All, the
almost flag offsets are set to
0.
Even though the offsets are
equivalent, the Empty and Almost-Empty flags have different
timing which means that the flags are not coincident. Similarly,
the Full and Almost-Full flags are not coincident after reset
because of timing.
These eight internal flags can be assigned to any of four
external flag pins (FLG
A
-FLG
D
) through Configuration Regis-
ter 4 (see Table 9). For the specific flag timings, see Figures
20-23.
The current state of all eight flags is available in the Status
Register.
Assignment
Code
0000
0001
0010
0011
0100
0101
0110
0111
1000
1001
1010
1011
1100
1101
1110
1111
Internal Flag Assigned to Flag Pin
A→B
Empty
A→B
Full
A→B
Almost-Empty
A→B
Almost-Full
B→A
Empty
B→A
Full
B→A
Almost-Empty
B→A
Almost-Full
A→B Empty
A→B Almost-Empty
A→B Full
A→B Almost-Full
B→A Empty
B→A Almost-Empty
B→A Full
B→A Almost-Full
2668 tbl 11
Table 9. Configuration Register 4 Internal Flag Assignments to
External Flag Pins
5.32
10
IDT [ INTEGRATED DEVICE TECHNOLOGY ]
