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Address decoding circuit using an OTP
When the size of the memory chip is small, the address decoding circuit for that chip is more complex. An address decoding circuit may need several chips. Since lowering chip count can reduce system cost, one can use an OTP to make several address decoding circuits. A low density OTP memory chip is very inexpensive. Let us use a 1Kx8 OTP to implement an address decoding circuit. The OTP can be programmed in such a way that an output pin gives the same signal for a range of input addresses. Therefore, each output pin can constitute a memory chip enable signal.
For example, in the above figure, the OTP should be programmed in such a way that all addresses on the memory chip 1 have a value of 0 in bit 3 of OTP. All addresses on the memory chip 2 have a value of 0 in bit 7 of OTP.