Chemestry Second Paper

১ম অধ্যায়	পরিসাবেশ রয়ন
২য় অধ্যায়	জৌব রসায়ন
৩য় অধ্যায়	পরিমানগত রসায়ন
৪র্থ অধ্যায়	তড়িত রসায়ন
৫ম অধ্যায়	অর্থনৈতিক রসায়ন
	সকল অধ্যায়ের গুরুত্বপুর্ণ তত্বসমুহ

2.5. Peripheral Interface Adapter (8255) 

Peripheral interface adapters are used to make a interface between the CPU and the peripheral devices. It is also known as I/O (Input / output) port. Because the CPU uses these devices to get input or give output to the external devices like printer, modem, mouse etc. For example the Intel 8255A is a general-purpose programmable I/O device designed to use with Intel microprocessors. It has 24 I/O pins, which can be individually programmed in groups of individual sizes. 

2.6. Timer (8253) 

You may have noticed that when the computer is off, its time counting is not off. The timer IC does this operation. It keeps the timing information of the computer continuously even if the computer is off. It is battery operated when the computer off. It has several counters, which counts the clock pulses generated by an external oscillator. As this timer IC is connected with the CPU through the data bus so the CPU can collect the counted value of clock pulses from the IC and convert the clock pulse count to seconds and minutes. The Intel 8253 is programmable counter/timer device designed for use as an Intel microcomputer peripheral. It is organized as 3 independent 16-bit counters, each with a count rate of up to 2.6 MHz. 

2.7. Floppy Disk Controller Chip (8272) 

Whenever a computer wants to interface with an outside device, it needs a controller board to act as a “go-between” to allow the outside device-a floppy, in this case-to talk with the CPU. XT-type machines generally had a separate controller board. AT-type machines usually put the floppy and hard disk controller function on the same board. Some motherboards (PS/2s, in particular) put the floppy controller function right on the motherboard. On most modern clones, the floppy controller is integrated on a single add-in card that serves as floppy controller, dual serial port, parallel port, joystick interface, and IDE host adapter. Whether your floppy controller is a separate board, part of the floppy/hard disk controller, or integrated into the motherboard, the main chip on a floppy controller board is probably the Zilog 765, NEC 765, or Intel 8272.