Simple and practical EPROM detection circuit

For a new EPROM, the data read out of each cell is FF.

This circuit is based on the characteristics of EPROM itself. The simplest method is used to read the value of each cell of the tested EPROM. If all are FF, it proves that it has been erased. The specific circuit is shown in the figure.

This circuit can test six common types of EPROM: 2716, 2732, 2764, 27128, 27256, 27512. Each type is selected by a dial switch and indicated by a light-emitting diode. The test result is displayed by another light-emitting diode. When it lights up, it means that it is not erased cleanly.

The working principle is as follows: First, the CD4040 (1) (2) is reset at the same time through the main reset switch S, so that the address points to the first unit of the EPROM to be tested, and the result indicator light is off. At this time, according to the model of the EPROM to be tested, press the corresponding button (S1~S6) and the corresponding model indicator light will light up. At this time, the square wave generated by the oscillator composed of CD4011 is used as the clock signal of CD4040, so that the address of the EPROM is continuously increased by 1. Since the control signals of the EPROM are all set to be valid, the result is read out by D0~D7. If a unit read out is not FF, CD4068 (1) will be reversed, and this state will be latched by the RS trigger CD4013, and the result indicator light will light up. When the test is completed, the address signal will feed this information back to the control part CD4011, making CD4068 (2) valid and CD4040 reset. The entire system is in the initial state again.

For 2716 and 2732, their packaging forms are different from the following ones, and the power supply part is located at the AB position of the following ones. In order to simplify the circuit and improve the compatibility of this circuit, we designed the power supply control circuit of 2716 and 2732, and connected it directly at the AB position, which is controlled by the two buttons S1 and S2 respectively.

This circuit has been put into practice with good results, low cost, easy production and debugging, and has great use value.