Circuit diagram of programmable digital IC tester is shown below.
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:
- The slave sends a ready bit to the master IC when it is ready to receive data.
- If the slave is ready, the master places the data on the data lines.
- A control bit gets set as soon the master transmits the data.
- The slave checks whether the bit is set, and then receives the data.
- Another control bit gets set as soon as the slave receives the data.
- 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.
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.
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.
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