Advanced RAM

Intoducation

• DRAMs commonly used as main memory in processor based embedded systems.
- high capacity, low cost.

• Many variations of DRAMs proposed.
- need to keep pace with processor speeds.
- FPM DRAM: fast page mode DRAM.
- EDO DRAM: extended data out DRAM.
- SDRAM/ESDRAM: synchronous and enhanced synchronous DRAM.
- RDRAM: rambus DRAM.

Basic DRAM

• Address bus multiplexed between row and column components.
• Row and column addresses are latched in, sequentially, by strobing ras (row address strobe) and cas (column address strobe) signals, respectively.
• Refresh circuitry can be external or internal to DRAM device.
- strobes consecutive memory address periodically causing memory content to be refreshed.
- Refresh circuitry disabled during read or write operation.



Note: In computer or memory technology, a strobe is a signal that is sent that validates data or other signals on adjacent parallel lines. In memory technology, the CAS (column address strobe) and RAS ( row address strobe ) signals are used to tell a dynamic RAM that an address is a column or row address.

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