MINIMUM MICRO CONTROLLER CONNECTIONS

A microcontroller is not alone in a circuit,it must be having supporting

components to make it functional.

1.a crystal(12MHZ)and two capacitors(33pF).

2.RESET connection(RC circuit).

3.EA pin connected HIGH to Vcc(only when internal memory is used).

so the minimum microcontroller configuration is as shown in the schematic

below.

MINIMUM MICROCONTROLLER CONFIGURATION:

click on image to enlarge

Download schematic pdf file here

note:keep this circuit in your memory we will encounter this minimum

configuration very often in our circuits.

EXTRA READING:

1.33pF capacitors are needed to remove unwanted ripple and stray oscillations.

2.crystal is needed to provide oscillations,which moves the instructions to

be executed by the CPU of microcontroller.greater is the crystal speed,

speeder the operation.generally a crystal of 12MHZ to

20MHZ can be used.it can be even high and is limited by microcontroller

fabrication.

3.RESET connection has RC elements which have characteristics of RC highpass

circuit.

4.when microcontroller is powered ON,the RC circuit generates a spike

(a triggering pulse)which makes RESET pin(9) logic'1' for small duration of

time.

when RESET is made high the microcontroller will reset and terminates

all acivities,and the program counter will point to

the first instruction of the program(0000 location of ROM) also all the

values in the registers will be lost.

5.each and every time the supply is switched ON the microcontoller RESETS with

this RC circuit.

6.in order for the RESET to be effective,it must have a minimum duration

of 2 machine cycles(2x12 crystal cycles)i.e 2x1.085uSec.so it must be high

for a minimum of 2 machine cycles before it goes low.

we discuss more about this machine cycles later.

7.a RC circuit with R=8.2k and C=10uF are used here in the circuit,which is

tested and gives our minimum duration of time for which the RESET must be high.

8.most of the 8051 family microcontrollers come with on chip ROM(EEPROM flash)

to store the programs.if the program is accesed from the internal ROM of micro

controller,then the EA pin is tied HIGH to Vcc.for family members such as

8031 there is no on chip ROM and the code is fetched from external ROM.

therefore for 8031 type the EA pin must be connected to LOW(GND),to indicate that

code is stored externally.EA stands for external access(pin 31).it is an input

pin and is connected to Vcc(for internal code access) or to GND(for external

access).it must not be left unconnected(floating).

*****any queries or comments ??? just post them here,or mail me,Thank you!!!!!!!!**********

-Regards

venkatesh