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Chapter 3: Memory Blocks in the Cyclone III Device Family

Clocking Modes

Cyclone III Device Handbook

December 2011

Altera Corporation

Volume 1

Clocking Modes

Cyclone III device family M9K memory blocks support the following clocking modes:

■

Independent

■

Input or output

■

Read or write

■

Single-clock

When using read or write clock mode, if you perform a simultaneous read or write to

the same address location, the output read data is unknown. If you require the output

data to be a known value, use either single-clock mode or I/O clock mode and choose

the appropriate read-during-write behavior in the MegaWizard Plug-In Manager.

1 Violating the setup or hold time on the memory block input registers might corrupt

the memory contents. This applies to both read and write operations.

1 Asynchronous clears are available on read address registers, output registers, and

output latches only.

Table 3–5 lists the clocking mode versus memory mode support matrix.

Independent Clock Mode

Cyclone III device family M9K memory blocks can implement independent clock

mode for true dual-port memories. In this mode, a separate clock is available for each

port (port A and port B). clock A controls all registers on the port A side, while clock

controls all registers on the port B side. Each port also supports independent clock

enables for port A and B registers.

I/O Clock Mode

Cyclone III device family M9K memory blocks can implement input or output clock

mode for FIFO, single-port, true, and simple dual-port memories. In this mode, an

input clock controls all input registers to the memory block, including data, address,

byteena

, wren, and rden registers. An output clock controls the data-output registers.

Each memory block port also supports independent clock enables for input and

output registers.

Table 3–5. Cyclone III Device Family Memory Clock Modes

Clocking Mode

True Dual-Port

Mode

Simple

Dual-Port

Mode

Single-Port

Mode

ROM Mode

FIFO Mode

Independent

——

—

Input or output

—

Read or write

—

——

Single-clock

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