hexadecimal display decoder

Decoders for converting a four bit binary code into a hexadecimal display are often few and far be- tween. With the aid of the PROM programmer featured elsewhere in this issue it is possible to solve the problem by programming a PROM to function as a hexadecimal display decoder. There is exactly enough memory space in the 82S23 PROM, which is a 32 x 8 bit device, for such a de- coder program. The eight outputs of the PROM control the seven segments of the display and the decimal point. When a logic "1" is present at the "blank" input the display will be turned off. The display in the circuit diagram is a MAN 4610A type. Other com- mon anode types are of course also suitable, but pin connections may be different. Before the PROM can fulfill its task it will have to be programmed. A suitable program is given in the table. If the data to be entered is inverted then, of course, common cathode displays can be used. In principle, the 74S188 (also a 32 x 8 bit PROM) is equally suitable. ...