DIGITAL IC TESTER

An Integrated Circuit tester (IC tester) is used to test Integrated Circuits (ICs). We can easily test any digital IC using this kind of an IC tester. For testing an IC, we need to use different hardware circuits for different ICs; like we need a particular kind of tester for testing a logic gate and another for testing flip flops or shift registers which involves more complication and time involved will also be more. So here’s an IC tester to overcome this problem. Unlike other IC testers, this is more reliable and easier since we don’t need to rig up different kind of circuits for different kind of ICs, each time we need to test them.

Unlike the IC testers available in the market today which are usually expensive, this IC tester is affordable and user-friendly. This IC tester is constructed using 8951 microcontroller along with a keyboard and a display unit. It can test digital ICs having a maximum of 24 pins. Since it is programmable, any number of ICs can be tested within the constraint of the memory available. This IC tester can be used to test a wide variety of ICs which includes simple logic gates and also sequential and combinational ICs like flip-flops, counters, shift registers etc. It is portable and easy to use.

The block diagram of the programmable digital IC tester is as shown in below. It consists of two 8951 microcontroller ICs, a 24-pin IC socket, a keyboard unit, a display unit and indicators.

To test a particular digital IC, one needs to insert the IC into the IC socket and enter the IC number using the keyboard and then press the “ENTER” key. The IC number gets displayed in the 7-segment display unit.

Four LEDs are provided as indicators. If the IC being tested is a logic gate, then each of the 4 indicator LEDs correspond to the 4 gates of the IC. In any other case wherein the inserted IC is not a logic gate, all the 4 LEDs work as a single indicator.

Digital IC Tester

Block diagram of Programmable Digital IC Tester:

Circuit diagram

The programmable digital IC tester consists of 2 8951 microcontroller. One is called master and the other slave. The master controls the slave and the working of the display and keyboard units. The slave IC is used for testing the IC inserted into the IC socket. Out of the four ports available in the 8951, three ports – port 0, port 1(Not all pins), port 2 are connected to the 24 pins of the IC socket. Port 3 is used for parallel communication between the slave and the master.

The keyboard and display units are interfaced with the master IC. Four indicators are also connected to the master IC. When we feed the number of the IC being tested, the number gets stored in the memory of the master IC and also gets displayed in the in the 7-segment display. The display unit is connected to the lower pins of port 0 of the master IC. The keyboard is connected to port 1 and the four indicators are connected to the port 1 of Slave IC.

Parallel communication is used between the master and the slave. There are four data lines and three control lines for transfer and control of data between the master and the slave. Port 3 of the slave IC and port 2 of the master IC are used for parallel communication.

To test a particular digital IC, one needs to insert the IC into the IC socket and enter the IC number using the keyboard and then press the “ENTER” key. The IC number gets displayed in the 7-segment display unit. The IC number gets transferred to the slave using parallel communication.

The process of parallel communication is as follows:

1. The slave sends a ready bit to the master IC when it is ready to receive data.
2. If the slave is ready, the master places the data on the data lines.
3. A control bit gets set as soon the master transmits the data.
4. The slave checks whether the bit is set, and then receives the data.
5. Another control bit gets set as soon as the slave receives the data.
6. A third control bit gets set whenever the slave is ready to accept another set of data.

As soon as the slave gets the IC number, it compares the IC number with the stored list and then goes to the corresponding service routine. The service routine checks the particular IC. Depending to the IC, it assigns some ports as input ports and some as output ports. It gives the corresponding inputs and checks for the output according to the IC logic. If the output is according to the IC logic, the slave sends the data to the master IC. If the IC is a logic gate, then the data will consist of 4 bits, where each bit corresponds to each gate of the IC. In case the IC is not a logic gate, the data consists of a single bit, which may be a ‘0’ or a ‘1’. Corresponding to these four bits, the master sets or resets the lower port of P3, which is connected to the indicators. Four LEDs are interfaced to the master IC as indicators. If the IC being tested is a logic gate, then each of the 4 indicator LEDs correspond to the 4 gates of the IC. In any other case wherein the inserted IC is not a logic gate, all the 4 LEDs work as a single indicator.

Using this IC tester, any digital IC can be tested provided its program is written. For a particular IC, the corresponding program must be written in the slave. The total number of ICs that can be tested using this IC tester, depends on the memory available in the slave. The 8951 microcontroller consists of a 4k ROM, using which around 150 ICs can be tested. To test more number of ICs, a microcontroller with an 8k ROM can be used.

The keyboard is provided with a ‘RESET’ button, which when pressed resets both the microcontrollers and the 4 shift registers. The shift registers require a low pulse to get reset, whereas the microcontrollers require a high pulse to get reset. To synchronize this, a NOT gate is used.

Display Unit:

The display unit is used to display the IC number. This unit consists of five common anode 7-segment displays, five 7447 ICs(BCD to 7-segment converter) and four 74194 ICs(4-bit bidirectional universal shift register).

Here, the shift registers are used in parallel load (parallel in parallel out) mode. These shift registers are used to shift the digits of the IC number. When the first digit is pressed, the master recognizes it and places it in the lower pins of port 0. These four bits are connected to the input of the first shift register and also to the input of the first 7447 IC. The 7447 is a BCD to 7-segment converter, which converts the four input bits (BCD) to their corresponding 7-segment codes.

The outputs of the 7447 are connected to the 7-segment displays. Hence the first digit gets displayed in the right-most 7-segment display. As the next number is typed in, the master gives a clock pulse to the shift registers to shift the data. Then the master places the second digit on the lower pins of port 0. Hence the new digit gets displayed in the right-most 7-segment display and the previous digit gets shifted to the left.

S0 and S1 of the 74194 IC are connected to +Vcc, to work in parallel mode. P3.4 of the master is connected to the clock pins of all the shift registers. These shift registers require a low to high clock pulse. The ‘RESET’ button provided in the keyboard resets all the shift registers. The common pins of the 7-segment display are connected to +Vcc.

The entire display section is shown in the figure below.

Circuit diagram of Display section

Keyboard section:

The keyboard section is as shown in the figure below. The keyboard is designed as a matrix and is interfaced to port 1 of the master IC. Here P1.0, P1.1, P1.2 are configured as input ports, and P1.3, P1.4, P1.5, P1.6 are configured as output ports. The keyboard consists of 10 digits as well as an ‘ENTER’ button.

Circuit diagram of Keyboard section

Software program for master IC:

setb p2.7
mov r0,#30h
mov p1,#0ffh
mov r7,#01
start: mov p0,#0 ;Clear first digit
wait: setb p1.3 ;Keyboard interfacing
setb p1.4 ;Enable all rows
setb p1.5
setb p1.6
jb p1.0,key ;Check whether key is pressed
jb p1.1,key
jb p1.2,key
jmp wait ;If not, check again

key: mov r2,#0a0h
d: djnz r2,d
mov r1,#01 ;Pressed digit
mov r2,#01
nextrow:cjne r2,#01,nextr1
setb p1.6 ;Enable first row
clr p1.5 ;Disable other rows
clr p1.4
clr p1.3
jmp over
nextr1: cjne r2,#02,nextr2
setb p1.5 ;Enable second row
clr p1.6 ;Disable other rows
clr p1.4
clr p1.3
jmp over
nextr2: cjne r2,#03,nextr3
setb p1.4 ;Enable third row
clr p1.5 ;Disable other rows
clr p1.6
clr p1.3
jmp over
nextr3: setb p1.3
clr p1.5 ;Enable fourth row
clr p1.4 ;Disable other rows
clr p1.6
over: jb p1.0,col1 ;If key is pressed in particular row, check
jb p1.1,col2 ; for corresponding column
jb p1.2,col3
mov a,#03
add a,r1
mov r1,a
inc r2
jmp nextrow

col1: jnb p1.0,over
jmp done
col2: jnb p1.1,over
inc r1
jmp done
col3: jnb p1.2,over
mov a,#02
add a,r1
mov r1,a
done: mov a,r1
cjne a,#0bh,enter
mov r1,#0
jmp down
enter: mov a,r1
cjne a,#0ch,down
jmp out
down: mov @r0,r1
inc r0
mov a,#01
xrl a,r7
jz noshift
clr p3.4
mov r2,#0ffh
here: djnz r2,here
setb p3.4

noshift: mov r7,#00
mov p0,r1
wait1: jb p1.0,wait1
jb p1.1,wait1
jb p1.2,wait1
mov r2,#0ffh
delay2: djnz r2,delay2
wait2: jmp wait

out: cjne a,#0ch,wait2
clr p2.4
mov r2,#0ffh
here1: djnz r2,here1
setb p2.4
mov a,#0
mov p0,a
out1: jb p1.0,out1
jb p1.1,out1
jb p1.2,out1
mov a,r0
subb a,#02
mov r0,a
mov a,@r0
swap a
mov r5,a
inc r0
mov a,@r0
add a,r5
mov r5,a
cjne r5,#0,nor
mov a,#1
jmp x
nor: cjne r5,#02,and
mov a,#2
jmp x
and: cjne r5,#08,or
mov a,#3
jmp x
or: cjne r5,#32h,xor
mov a,#4
jmp x
xor: cjne r5,#86h,else
mov a,#5
jmp x
else: mov a,#0fh
x: mov p2,#00
jnb a.0,nextb1
setb p2.0

nextb1: jnb a.1,nextb2
setb p2.1
nextb2: jnb a.2,nextb3
setb p2.2
nextb3: jnb a.3,ove
setb p2.3
ove: clr p2.7

end: jmp end

Software program for slave IC:

mov p0,#0
mov p2,#0
mov p1,#0
mov r0,#0ffh
del: djnz r0,del
setb p3.7
wait:jb p3.7,wait
mov a,#0
setb p3.0
setb p3.1
setb p3.2
setb p3.3
jnb p3.0,nextb1
setb a.0
nextb1: jnb p3.1,nextb2
setb a.1
nextb2: jnb p3.2,nextb3
setb a.2
nextb3: jnb p3.3,over
setb a.3

over:cjne a,#1,next2 ;NAND
call gateic
mov a,r3
rl a
mov r2,#07h
xrl a,r2
jnz checkg12
setb p1.2

checkg12: mov a,r4
rl a
mov r2,#07h
xrl a,r2
jnz checkg13
setb p1.3

checkg13: mov a,r5
rl a
mov r2,#07h
xrl a,r2
jnz checkg14
setb p1.4

checkg14: mov a,r5
rl a
mov r2,#07h
xrl a,r2
jnz end2
setb p1.5
jmp end2

next2: cjne a,#2,next3 ;NOR
call gateic
mov a,r3
rl a
mov r2,#01h
xrl a,r2
jnz checkg22
setb p1.2

checkg22: mov a,r4
rl a
mov r2,#01h
xrl a,r2
jnz checkg23
setb p1.3

checkg23: mov a,r5
rl a
mov r2,#01h
xrl a,r2
jnz checkg24
setb p1.4

checkg24: mov a,r5
rl a
mov r2,#01h
xrl a,r2
jnz end1
setb p1.5
end2: jmp end1

next3: cjne a,#3,next4 ;AND
call gateic
mov a,r3
rl a
mov r2,#08h
xrl a,r2
jnz checkg32
setb p1.2

checkg32: mov a,r4
rl a
mov r2,#08h
xrl a,r2
jnz checkg33
setb p1.3

checkg33: mov a,r5
rl a
mov r2,#08h
xrl a,r2
jnz checkg34
setb p1.4

checkg34: mov a,r5
rl a
mov r2,#08h
xrl a,r2
jnz end1
setb p1.5
jmp end1

next4: cjne a,#4,next5 ;OR
call gateic
mov a,r3
rl a
mov r2,#0Eh
xrl a,r2
jnz checkg2
setb p1.2

checkg2: mov a,r4
rl a
mov r2,#0Eh
xrl a,r2
jnz checkg3
setb p1.3

checkg3: mov a,r5
rl a
mov r2,#0Eh
xrl a,r2
jnz checkg4
setb p1.4

checkg4: mov a,r5
rl a
mov r2,#0Eh
xrl a,r2
jnz end3
setb p1.5

end1: jmp end3

next5: cjne a,#5,end2 ;XOR
call gateic
mov a,r3
rl a
mov r2,#06h
xrl a,r2
jnz checkg52
setb p1.2

checkg52: mov a,r4
rl a
mov r2,#06h
xrl a,r2
jnz checkg53
setb p1.3

checkg53: mov a,r5
rl a
mov r2,#06h
xrl a,r2
jnz checkg54
setb p1.4

checkg54: mov a,r5
rl a
mov r2,#06h
xrl a,r2
jnz end
setb p1.5
end3: jmp end

gateic: mov r0,#25h
mov a,#24h
mov @r0,a
inc r0
mov a,#2Dh
mov @r0,a
inc r0
mov a,#36h
mov @r0,a
inc r0
mov a,#3Fh
mov @r0,a
mov r1,#30h
mov a,#92h
mov @r1,a
inc r1
mov a,#B6h
mov @r1,a
inc r1
mov a,#DAh
mov @r1,a
inc r1
mov a,#FEh
mov @r1,a
mov r0,#25h
mov r1,#30h
mov r3,#0
mov r4,#0
mov r5,#0
mov r6,#0
mov r7,#4

nextcnd:mov a,@r0
inc r0
mov p0,a
mov a,r3
jnb p0.2,g2
setb a.3
g2: rr a
mov r3,a
mov a,r4
jnb p0.5,g3
setb a.3
g3: rr a
mov r4,a
mov a,@r1
inc r1
mov p2,a
mov a,r5
jnb p2.1,g4
setb a.3
g4: rr a
mov r5,a
mov a,r6
jnb p2.4,overcnd
setb a.3
overcnd:rr a
mov r6,a
djnz r7,nextcnd
ret

end: clr p3.6

stop: jmp stop

http://electrofriends.com/projects/microcontrollers/digital-ic-tester/