RAM tester

7-70 elektor july/august 1980 IC4 74155 8 51 3 13 11 8 9 11 6 N10 2 IC7 7493 3 10 8 9 12 IC 5 7493 21 3 10 11 Ien IC1 IC2 N1 ... N6 = 1%7400 =IC1+IC2 N7 ... N12 = 7414 = IC3 73 RAM tester 0 N7 4 rwinpTrmn-t.l s0 klisRieset 470(1 N12 5V 5 2102 MI1M.TI.1-111111111111 6 16 2 7 91 3 11 8 9 12 IC 6 7493 21 3 10 IN= 0 5V 5V 5V 80508 2 One of the most popular memory ICs at present is the 2102 — a 1 k random access memory. In spite of its popu- larity, a simple tester for this type of IC is virtually unknown. The circuit described here does the job easily - and cheaply. The operation is quite straight- forward, as illustrated in the flow chart given in figure 1. First a 0 is written into all memory locations, after which the IC is switched into the "read" mode to check whether there is indeed a 0 at each address. If a logic 1 is found anywhere, a red LED lights to indicate that the IC is defective. Assuming that no fault is found, however, the next step is to write a 1 into all memory l...