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Without knowing the clock frequency it is impossible to state if one set of timings is "faster" than another. For example, DDR3-2000 memory has a 1000 MHz clock frequency, which yields a 1 ns clock cycle. With this 1 ns clock, a CAS latency of 7 gives an absolute CAS latency of 7 ns. Faster DDR3-2666 memory (with a 1333 MHz clock, or 0.75 ns ...
Double Data Rate 5 Synchronous Dynamic Random-Access Memory (DDR5 SDRAM) is a type of synchronous dynamic random-access memory. Compared to its predecessor DDR4 SDRAM , DDR5 was planned to reduce power consumption, while doubling bandwidth . [ 5 ]
The 8n prefetch architecture is combined with an interface designed to transfer two data words per clock cycle at the I/O pins. A single read or write operation for the DDR4 SDRAM consists of a single 8n-bit-wide 4-clock data transfer at the internal DRAM core and 8 corresponding n-bit-wide half-clock-cycle data transfers at the I/O pins. [20]
Column address strobe latency, also called CAS latency or CL, is the delay in clock cycles between the READ command and the moment data is available. [1] [2] In asynchronous DRAM, the interval is specified in nanoseconds (absolute time). [3] In synchronous DRAM, the interval is specified in clock cycles.
It is legal to stop the clock entirely during this time for additional power savings. Finally, if CKE is lowered at the same time as an auto-refresh command is sent to the SDRAM, the SDRAM enters self-refresh mode. This is like power down, but the SDRAM uses an on-chip timer to generate internal refresh cycles as necessary.
The GDDR5 interface transfers two 32-bit wide data words per write clock (WCK) cycle to/from the I/O pins. Corresponding to the 8N-prefetch, a single write or read access consists of a 256-bit wide two CK clock cycle data transfer at the internal memory core and eight corresponding 32-bit wide one-half WCK clock cycle data transfers at the I/O ...
These numbers represent t CL-t RCD-t RP-t RAS in multiples of the DRAM clock cycle time. Note that this is half of the data transfer rate when double data rate signaling is used. JEDEC standard PC3200 timing is 3-4-4-8 [ 38 ] with a 200 MHz clock, while premium-priced high performance PC3200 DDR DRAM DIMM might be operated at 2-2-2-5 timing.
Address and control signals are still sent to the DRAM once per clock cycle (to be precise, on the rising edge of the clock), and timing parameters such as CAS latency are specified in clock cycles. Some less common DRAM interfaces, notably LPDDR2, GDDR5 and XDR DRAM, send commands and addresses using double data rate.