Black and white Computer

The following is the characteristic of Read Only Memory (ROM). Non-volatile(data remain even the power cut off) Mainly using in Embedded System Only can write the information once at time of manufacture Can only read the data but no write therefore call Read Only Memory It is directly accessible. Example of type: Programmable ROM Erasable Programmable ROM Electrically Erasable Programmable ROM  Cheaper than RAM Read rate is slow than RAM The logic value is 0 if the transistor is connected to ground like the picture above. READ OPERATION First ,the word line is activate to close the transistor .After the transistor is close,the voltage on the bit line drop near zero if there is a connection between the transistor and ground,else the bit line remain at high voltage which mean a logic value 1. The sense circuit at the end of the bit line generates the proper output values.

The diagram below is illustrate Static Random Access Memory (SRAM)Cell for the explanation. SRAM cell is make up of 2 inverters are cross-connected to form a latch .The latch is connected to 2 bit line by transistor T1 and T2 . T1 and T2 can switch opened or closed under control of word line.When word line is ground level, the transistors are turned off and the latch retrains its state. During the Read Operation ,Word line is activated to close switches T1 and T2 . If the cell is in state 1; the signal on b line is high and the signal on b’ line is low.The opposite is true if the cell is in state 0.Thus, b and b’ are always complements of each other’s. The sense /write circuit at the end of the two bit line monitors their state and sets the corresponding output accordingly. While in Write Operation ,the Sense/Write circuit drives bit lines b and b’, instead of sensing their state.It places the appropriate value on bit line b and its complement on b’ and activate the word ...

In Dynamic Random Access Memory CELL , transistor acts as a switch to Close (allowing current to flow) when voltage applied in address line or Open (no current flow) when no voltage applied in address line.Address Line also known as word line .Which use to signal the transistor to close or open. During the Write operation ,a voltage is applied on the bit line and a signal applied to the address line to close the transistor.Then the voltage applied on the bit line will transfer to capacitor and store in the capacitor However the capacitor has tendency to discharge and has to refresh to maintain the bit. While in Reading Operation ,the instruction find the bit store using the address line to read the data or bit. When the address line is selected ,the transistor turns on and the charge stored on the capacitor is fled out onto a bit line and to sense amplifier. Sense amplifiers compare the capacitor voltage to reference value to determine the logic 1 or logic 0.The read out from ...