External Memory Interface Handbook Volume 2: Design Guidelines

ID 683385
Date 5/08/2017
Document Table of Contents

1.1.3. DDR, DDR2, DDR3, and DDR4 SDRAM Command and Address Signals

Command and address signals in SDRAM devices are clocked into the memory device using the CK or CK# signal. These pins operate at single data rate (SDR) using only one clock edge. The number of address pins depends on the SDRAM device capacity. The address pins are multiplexed, so two clock cycles are required to send the row, column, and bank address.

For DDR, DDR2, and DDR3, the CS#, RAS#, CAS#, WE#, CKE, and ODT pins are SDRAM command and control pins. For DDR3 SDRAM, certain topologies such as RDIMM and LRDIMM include RESET#, PAR_IN (1.5V LVCMOS I/O standard), and ERR_OUT# (SSTL-15 I/O standard).

The DDR2 SDRAM command and address inputs do not have a symmetrical setup and hold time requirement with respect to the SDRAM clocks, CK, and CK#.

Although DDR4 operates in fundamentally the same way as other SDRAM, there are no longer dedicated pins for RAS#, CAS#, and WE#, as those are now shared with higher-order address pins. DDR4 still has CS#, CKE, ODT, and RESET# pins, similar to DDR3. DDR4 introduces some additional pins, including the ACT# (activate) pin and BG (bank group) pins. Depending on the memory format and the functions enabled, the following pins might also exist in DDR4: PAR (address command parity) pin and the ALERT# pin.

For Intel® SDRAM high-performance controllers in Stratix III and Stratix IV devices, the command and address clock is a dedicated PLL clock output whose phase can be adjusted to meet the setup and hold requirements of the memory clock. The command and address clock is also typically half-rate, although a full-rate implementation can also be created. The command and address pins use the DDIO output circuitry to launch commands from either the rising or falling edges of the clock. The chip select CS#, clock enable CKE, and ODT pins are only enabled for one memory clock cycle and can be launched from either the rising or falling edge of the command and address clock signal. The address and other command pins are enabled for two memory clock cycles and can also be launched from either the rising or falling edge of the command and address clock signal.

In Arria II GX devices, the command and address clock is either shared with the write_clk_2x or the mem_clk_2x clock.

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