Altera Cyclone IV, Device Handbook

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Chapter 3: Memory Blocks in Cyclone IV Devices 3–7
Memory Modes
November 2011 Altera Corporation Cyclone IV Device Handbook,
Volume 1
Asynchronous Clear
Cyclone IV devices support asynchronous clears for read address registers, output
registers, and output latches only. Input registers other than read address registers are
not supported. When applied to output registers, the asynchronous clear signal clears
the output registers and the effects are immediately seen. If your RAM does not use
output registers, you can still clear the RAM outputs using the output latch
asynchronous clear feature.
1
Asserting asynchronous clear to the read address register during a read operation
may corrupt the memory content.
Figure 3–5 shows the functional waveform for the asynchronous clear feature.
1
You can selectively enable asynchronous clears per logical memory using the
Quartus II RAM MegaWizard
™
Plug-In Manager.
f
For more information, refer to the RAM Megafunction User Guide .
There are three ways to reset registers in the M9K blocks:
■ Power up the device
■ Use the
aclr
signal for output register only
■ Assert the device-wide reset signal using the DEV_CLRn option
Memory Modes
Cyclone IV devices M9K memory blocks allow you to implement fully-synchronous
SRAM memory in multiple modes of operation. Cyclone IV devices M9K memory
blocks do not support asynchronous (unregistered) memory inputs.
M9K memory blocks support the following modes:
■
Single-port
■ Simple dual-port
■ True dual-port
■ Shift-register
■
ROM
■ FIFO
Figure 3–5. Output Latch Asynchronous Clear Waveform
aclr
aclr at latch
clk
q
a1 a0 a1
a2