05-03-2013, 04:02 PM
Memory components
Memory components.ppt (Size: 359.5 KB / Downloads: 27)
Working of Internal organization of memory
Data stored in 2 Dimensional array of memory cell.
So, the n bit address received is split into row & column address n=r+c.
R & C select a particular memory cell
R/w’ controls the data transfer.
Data is controlled by enable signal.
Random-access memory
RAM can be read or written.
Two types of RAM:Static RAM & Dynamic RAM.
Dynamic RAM is dense(more DRAM can be put on a single chip), requires refresh.
Synchronous DRAM is dominant type(Normal DRAM plus a Clock).
SDRAM (Synchronous DRAM)uses clock to improve performance, pipeline memory accesses.
Static RAM is faster, less dense, consumes more power.
Read-only memory
ROM’s are Preprogrammed with fixed data.
Flash is dominant form of field-programmable ROM.
Electrically erasable, must be block erased.
Random access, but write/erase is much slower than read.
NOR flash is more flexible.
NAND flash is more dense.
Flash writing
Write is much slower than read.
1.6 ms write, 70 ns read.
Blocks are large (approx. 1 Mb).
Writing causes wear that eventually destroys the device.
Modern lifetime approx. 1 million writes.
COMPONENT INTERFACING
Width of the memory is selected by placing RAM’s in parallel
After determining particular memory for application , select particular RAM depending on availability and cost.
CE’s signal is permanently wired to ground so that chip is always enabled
Evaluation boards
Designed by CPU manufacturer or others.
Includes CPU, memory, some I/O devices.
Provide complete solution or equivalent to it.
CPU manufacturer often gives out evaluation board netlist (design)---can be used as starting point for your custom board design.
Breakpoint handler actions
Save registers.
Allow user to examine machine.
Before returning, restore system state.
Safest way to execute the instruction is to replace it and execute in place.
Put another breakpoint after the replaced breakpoint to allow restoring the original breakpoint.