programmable function generator

The circuit shown here will generate pre-programmable periodic wave-forms. The waveform is stored digitally in two 256 x 4 bit RAMs which are connected in parallel to form a single 256 x 8 bit memory. The output waveform is obtained by repeatedly cycling through the contents of each of the 256 memory locations. The resulting digital signal is fed to a D/A converter and finally to a lowpass filter (not present in the circuit described here) to remove the clock frequency components. The address bus is clocked via an 8-bit binary counter by the clock oscillator IC8. The frequency of the output signal is one twelfth that of the clock frequency.