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as more and more memory is squeezed onto a single chip, the number of address to address it also increases. It is often inconvenient to gave large numbers of address pins on a chip. Devise a way to address 2^n words of memory using fewer than n pins.

please help!

2006-09-26 17:06:01 · 3 answers · asked by Anonymous in Computers & Internet Programming & Design

3 answers

Dealt with this problem many, many moons ago.

One obvious solution is to use address lines for multiple address bits.

Assume that you use only 2^(n-1) address lines. You could put the first 2^(n-1) bits on the first cycle, and the second 2^(n-1) bits on the second cycle. The first set of bits would be latched internally, and combined with the second set to create the full address.

Depending on how you implement it, you may require the addition of one or more line to indicate which half of the address is being sent, but you should still reduce the number of lines required.

This can be taken to the extreme where only a single address bit is written per cycle - effectively using a serial transmission of the address.

The downside to this is that it will take longer to read and write to memory as more than one cycle will be required to write the address to the chip.

2006-09-26 21:03:32 · answer #1 · answered by brunt 4 · 0 0

multiplex the address lines. Say there are 32 address lines on a chip. if you multiplex the lower 16 addresses with the upper 16 address, you now only need 16 pins for addressing. the downside is it takes more time to read and write to memory.

the Intel 8 bit microcontroller does a similar thing to reduce pin count. except it multiplexes the lower 8 address lines with the 8 data lines.

2006-09-27 09:18:25 · answer #2 · answered by justme 7 · 0 0

You see, I havent encountered that problem before in my digital design, because 2^n is really the number pins needed for n-bits. But a hint, perhaps you could use a different number system for addressing, or perhaps you could create a toggle pin, but using this, you will be needing another clock pulse for the next upper sets of bits.

2006-09-27 02:05:32 · answer #3 · answered by Edgar Allan P 2 · 0 0

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