Asynchronous Clear; Memory Modes - Altera Cyclone IV Device Handbook

Chapter 3: Memory Blocks in Cyclone IV Devices

Memory Modes

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
Figure 3–5. Output Latch Asynchronous Clear Waveform
1
You can selectively enable asynchronous clears per logical memory using the
Quartus II RAM MegaWizard
f
For more information, refer to the
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
■
November 2011 Altera Corporation
shows the functional waveform for the asynchronous clear feature.
clk
aclr
aclr at latch
q
a1
a2
™
Plug-In Manager.
RAM Megafunction User
a0 a1
Guide.
Cyclone IV Device Handbook,
Volume 1
3–7