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I'm reading the datasheet of a PSRAM (available here). In the top-right hand corner all the pins are listed. Some of the pin names end with a hash, e.g. LB#, OE#.

What does the # notation mean for pins?

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I suppose it means active-low logic, usually indicated by an overscore. Signals like WE#, CE#, LB# and UB# are typically active-low. In datasheets you'll see them as \$\overline{\mathrm{WE}}\$, \$\overline{\mathrm{CE}}\$, \$\overline{\mathrm{LB}}\$ and \$\overline{\mathrm{UB}}\$.

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    \$\begingroup\$ And the logic behind this is '!' or '#' or an over-score all invert the logic. So when the pin is high, it means it is "Not what ever the pin name is" which is the same as saying it is active-low. \$\endgroup\$
    – Kellenjb
    Apr 12 '12 at 13:00
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    \$\begingroup\$ Another one I see is a leading ~ or a trailing _N. \$\endgroup\$ Apr 12 '12 at 15:58
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    \$\begingroup\$ @Brian - or a leading "\" (or "/", I'm not sure) \$\endgroup\$
    – stevenvh
    Apr 12 '12 at 16:00
  • \$\begingroup\$ @stevenh: Yes, that can be there. But be careful; \ is a special character to some tools. \$\endgroup\$ Apr 12 '12 at 16:13
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    \$\begingroup\$ @BrianCarlton - A leading \ in Altium causes the schematic editor to draw a line over the text (e.g. an overscore). So it may actually do what you want. \$\endgroup\$ Apr 12 '12 at 21:19

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