Address pins

TC

I have had this time keeper sitting around for some time now and I would like to use it. It has 15 address pins, I am looking to only access address 7FFF8h-7FFFh. I am not understanding what pins I can tie to VCC. Is it A0 – A11 tide to VCC? Or, is it A3 – A14 tied to VCC?
http://eu.st.com/stonline/products/literature/ds/6845.pdf
TC

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We all make mistakes when we are young………That’s why paste is edible!

PJAllen

A14 is the most significant bit, A0 is the least.
I take it you want to change A0, A1, A2, so you would tie A3 through A14 high (pull them up via 10K resistors.).
····· A14·············· A0
7FF8·· 111 1111 1111 1000
7FFF·· 111 1111 1111 1111

TC

Thanks PJ, one of these days I will understand MSB - LSB. I have not found a easy way to understand it.

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We all make mistakes when we are young………That’s why paste is edible!

PJAllen

What'll it take to muster your understanding?

[noparse][[/noparse] Good luck with the paste. ]

TC

PJ, I have trouble getting my paste filled brain around the idea of reading backward.
I am used to 0, 1, 2, 3… but when I look at a datasheet it says 7, 6, 5, 4… And you have to start at 7 not 0.

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We all make mistakes when we are young………That’s why paste is edible!

PJAllen

Binary numbers are read left to right, decimal numbers are read left to right; it's the same principle, the most significant digit is that furthest to the left and the least significant is that furthest to the right.·

A0 is the least (zero is the least).· Get with the plan, man.

TC

now I get it, DUH!!! so no mater what the datasheet says A0 allways equals LSB thanks

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We all make mistakes when we are young………That’s why paste is edible!