[SOLVED] Un-used memory I/O data pins, what to do?

Hey all,

I've been told it's a good practice to not leave floating pins.

Here's a situation:

I have 16-bit SRAM, but my data bus uses only 12 bits. What do I do with the remaining 4 data input/output pins on the SRAM chip? I understand a pull up or down resistor would be good for input, but would it still be good if the pins are output as well?

Please give advice. Thanks.

It is recommended to make the un-used IO pins as outputs and set them to either high or low otherwise leave them as inputs and do the pull up or down connection.

refer the note from microchip on page 4 for your reference.

https://ww1.microchip.com/downloads/en/devicedoc/01146b_chapter 2.pdf

hi
from my point of view , best way to make unsed I/O as input and tied them to either vcc or vss

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hobbyckts said:

It is recommended to make the un-used IO pins as outputs and set them to either high or low otherwise leave them as inputs and do the pull up or down connection.

refer the note from microchip on page 4 for your reference.

https://ww1.microchip.com/downloads/en/devicedoc/01146b_chapter 2.pdf

Click to expand...

Nice information thanks for sharing

hobbyckts said:

It is recommended to make the un-used IO pins as outputs and set them to either high or low otherwise leave them as inputs and do the pull up or down connection.

refer the note from microchip on page 4 for your reference.

https://ww1.microchip.com/downloads/en/devicedoc/01146b_chapter 2.pdf

Click to expand...

I think you misread my post. This is SRAM memory. I can't set the state of individual data pins of the chip, its a 16-bit data bus, all 16-pins switch state between input and output at the same time, but only 12 in my design are connected to a circuit, which leaves 4 floating. The bus is either input (when write enable is asserted) or output (when write enable is not asserted and output enable is asserted). I can't set those individual pins. I can't. SRAM is not an MCU FYI!!! To make it more clear, those pins switch between input and output during use, they are both.

Pins on memory are not programmable!!! And they can't be just input or just output, they are both! That's what makes the question trickier. The memory switches between input and output states during use.

tasuki said:

hi
from my point of view , best way to make unsed I/O as input and tied them to either vcc or vss

Click to expand...

So you say I should have output drivers of SRAM drive the ground...? Sounds like a good way to burn a chip.

What both of you say sounds strange, and dangerous.

Here's the chip in question:
https://www.mouser.com/ds/2/198/61WV102416ALL-258682.pdf

Pull them high or low through a resistor of say 10K. Plenty low enough in value to ensure the pin doesn't float when an input but high enough that it doesn't waste too much current if in output mode. Bear in mind that after a write cycle at the current address, the pin will read back at the level set by the resistor anyway so the current through it will be minimal.

Brian.

betwixt said:

Pull them high or low through a resistor of say 10K. Plenty low enough in value to ensure the pin doesn't float when an input but high enough that it doesn't waste too much current if in output mode. Bear in mind that after a write cycle at the current address, the pin will read back at the level set by the resistor anyway so the current through it will be minimal.

Brian.

Click to expand...

Perfect. The answer I was looking for. Thanks!