8284 (Clock Generator)

Clock Generator 8284

• The 8284A is an integrated circuit designed

specifically for use with the 8086/8088 microprocessors.

• Without the clock generator, many additional

circuits are required to generate the clock (CLK) in

an 8086/8088-based system.

• The 8284 is an 18 pin integrated circuit , designed

specifically for use with 8086 microprocessor.

This circuit provides the following basic functions or

signals

• clock generation,

• RESET synchronization,

• READY synchronization.

• TTL level peripheral clock signal

Pin Diagram

Pin Description

• CSYNC: The clock synchronization pin is used

whenever the EFI input provides synchronization in

systems with multiple processors. If the internal

crystal oscillator is used, this pin must be ignored.

• PCLK: The peripheral clock signal is one-sixth the

crystal or EFI input frequency, and has a 50-percent

duty cycle. The PCKL output provides a clock signal;

to the peripheral equipment in the system.

AEN1 & AEN2 :

• The address enable pins are provided to qualify the bus ready signal, RDY1 & RDY2 . These two pins are used to cause wait state, along with RDY1 & RDY2 inputs.

• Wait state are generated by the READY pin of the

8086 microprocessor which is controlled by these

two pins.

• RDY1 & RDY2: The bus ready inputs are provided,

in conjuction with the AEN1 & AEN2 pins, to cause

wait state in 8086 based system.

READY:

• READY is an output pin that connects to the

8086/8088 READY input.

• This signal is synchronized with the RDY1 and RDY2

Inputs.

• CLK: Provides CLK input signal to the 8086/8088

microprocessors and other components in the

system.

• GND: Connects to ground.

• Vcc : Connects to +5.0V with a tolerance of +10

percent.

RESET:

•The RESET output connects to the

8086/8088 RESET input pin.

• RES (Reset input): Active low input. Often connects

to an RC network that provides power -on resetting.

• OSC (Oscillator): TTL level signal output. Provides

an EFI input to other 8284A clock generators in

some multiple processor systems.

F/C(Frequency/Crystal select):

• It chooses the clocking source for the 8284A.

• F/C=1(high), an external clock is provided to the

EFI input pin.

• F/C=0(low), an external crystal oscillator

connected to X1 and X2 provides the clock.

EFI(External Frequency Input):

• It is used when F/C pin is set to high.

• It Supplies the timing whenever the F/C is high.

X1 & X2(Crystal inputs):

• An external crystal oscillator is connected to these

inputs.

• It is used as the timing source for the clock

generator and all its functions.

TNK(TANK):

• TNK stands for tank, these three inputs are interfaced to the internal oscillator of 8284.