AL4CS211/AL4CS221/AL4CS231/AL4CS241/AL4CS251
AL4CS211/AL4CS221/AL4CS231/AL4CS241/AL4CS251
December 14, 2001
12
9.0 Multiple Devices Bus Expansion and Cascading
9.1 Width Expansion Configuration
Simply connecting the corresponding input controls signals of multiple devices may increase data bus
width. A composite flag should be created for each of the end-point status flags (/EF and /FF). The
partial status flags (/PAE and /PAF) can be detected from any one device. Figure 15 demonstrates an
18-bit word width data bus by using two AL4CS211/221/231/241/251s. Any word width expansion
can be attained by adding additional AL4CS211/221/231/241/251s. When these devices are in a
Width Expansion Configuration, the Read Enable 2 (/REN2) control input can be grounded (see
Figure 15). In this configuration, theWriteEnable2<Load> (WEN2</LD>) pin is set LOW at Reset so
that the pin operates as a control to load and read the programmable flag offsets.
AL4CS2x1
/WEN1
WCLK
Q[8:0]
WEN2
/PAE
RCLK
/REN1
/OE
/PAF
AL4CS2x1
/WEN1
WCLK
Q[8:0]
WEN2
/PAE
RCLK
/REN1
/OE
/PAF
Write Clock
Write Enable
Write Enable2
Programmable
Write Controls
Write Controls
Read Controls
Read Clock
Read Enable
Output Enable
Programmable
Read Controls
Empty Flag/
Output Ready
18-Bit Data In Bus
18-Bit Data Out Bus
Full Flag/
Input Ready
Figure 2. Multiple FIFO memory
with programmable flags used in depth expansion configuration
9.2 Depth Expansion
The depth expansion of AL4CS211/221/231/241/251 is also possible. The existence of two enable
pins on the read and write port allow depth expansion. The Write Enable 2<Load> pin is used as a
second write enable in a depth expansion configuration thus the programmable flags are set to the
default values. Depth expansion is possible by using one enable input for system control while the
other enable input is controlled by expansion logic to direct the flow of data. A typical application
would have the expansion logic alternate data access from one device to the next in a sequential
manner. These FIFOs operate in the Depth Expansion configuration when the following conditions
are met:
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