The data generator offers a simple means of testing a circuit. It does need software and all the components are readily available. The design is based on the timing of a Type SDA3002 circuit. In contrast to the two-wire I2C format, a three-wire connection is used.If only one fixed data word needs to be sent. DIP switches S2 and S3 and the eightfold pull resistors arrays may be omitted the input of IC3 and IC4are then hold at fixed levels.
The generator is based on two cascaded shift register IC3 and IC4 that are used as 16-bit register parallel to serial converters.
The clock is provided by IC2, which is started by setting bistable IC1a.bwith press button switch S1. When this switch is pressed a 100 pulse is applied via differentiating network R1 – C1 to set input of bistable. The capacitor is discharged by via R2. the pulse duration is not changed by keeping S1 is depressed this is necessary because if it were to exceed a half clock period the timing would go astray. The output of IC1b is the enable signal for the circuit to be tested. the start pulse is used also to load the logic levels set with the DIP switches on to shift registers. The registers accept the parallel data as long as the signal at there pin1 is low. This is another reason that the start pulse has to be short.
The start signal begins the entire test cycle-see the timing diagram in Fig2: output 23 of IC2 id inverted by IC1d to provide the clock for shift registers. This ensures that D0 is present at the output for an entire clock period (1.25 ms).
After the output of 23 of IC2 has been high 18- times the bistable is reset and the enable line is pulled low by 23 of IC1 which is connected to output 25 and 28 of IC2. This completes the cycle.
In this example, 18 bits are shifted. Two MSBs are determined by the serial input of IC3. If this input is high D16 and D17 are ‘1’ If these bits are required to be variables. One or two additional bistables connected as shift register must be added.The current drawn by generator determined primarily by pull-down resistor is very low if all bits are high it is about 80. After S1 has been pressed. The Oscillator is started briefly which doubles the current.