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Anonymous
Not applicable

In my application, to fit in the same software of previous version IC, we are using S29AL008 in word mode but only 8 out of 16 data pins are used. So, other 8 data pins are left open. The question is whether I should leave this pins floating (risky choice as they are bidirectional) or should I pull up/down those pins? If pull up/down is used what will be the value of the resistor as I am little bit unsure about the maximum sink current of data pins?

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1 Solution
AlbertB_56
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500 replies posted 50 likes received 250 replies posted

Hello Saikat,

Thank you for contacting Cypress Semiconductor.

It is a good general design practice to pull the unused I/O pins to LOW with a 4.7K to 10K ohm resistor.

However, I do not quite understand your application's FLASH configuration.  If your previous application S/W was configured

using x8 (BYTE) mode, then all that is required is to tie the BYTE# pin to LOW on the S29AL008J, as the higher order of I/O's

will be tri-stated, and no conditioning or pull-up/pull-down is needed.  If your previous application S/W was configured using

x16 (WORD) mode, then all that is required is to pull the BYTE# pin to HIGH on the S29AL008J, as all of the I/O's will used

for bi directional data transfer.

 

Hope this helps...

Best regards,

Albert

Cypress Semiconductor

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5 Replies
AlbertB_56
Moderator
Moderator
Moderator
500 replies posted 50 likes received 250 replies posted

Hello Saikat,

Thank you for contacting Cypress Semiconductor.

It is a good general design practice to pull the unused I/O pins to LOW with a 4.7K to 10K ohm resistor.

However, I do not quite understand your application's FLASH configuration.  If your previous application S/W was configured

using x8 (BYTE) mode, then all that is required is to tie the BYTE# pin to LOW on the S29AL008J, as the higher order of I/O's

will be tri-stated, and no conditioning or pull-up/pull-down is needed.  If your previous application S/W was configured using

x16 (WORD) mode, then all that is required is to pull the BYTE# pin to HIGH on the S29AL008J, as all of the I/O's will used

for bi directional data transfer.

 

Hope this helps...

Best regards,

Albert

Cypress Semiconductor

Anonymous
Not applicable

Hello Albert,

Thanks for your reply.

The reason for using word mode is earlier we were using AM29LV010B as boot flash which has 8 data pins. Now, the command definition table of AM29LV010B matches with S29AL008J in word mode. So, to avoid any software change, we are planning to use the flash in word mode but with 8 data pins.


One question is, can I pull the unused I/O to high (as that is convenient in that particular board in terms of PCB layout)? If yes, what should be the resistor value, can it be 4.7k or 10k for that as well?


Regards,
Saikat.

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AlbertB_56
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500 replies posted 50 likes received 250 replies posted

Hello Saikat,

FYI :  The Am29LV010B has a 32-pin TSOP package, and the S29AL008J has a 48-pin TSOP package. 
These two TSOP package pin-assignments are not compatible.  In regards to the S29AL008J I/O's (DQ15-DQ8),

these I/O can be tied to Logic HIGH, via 4.7 to 10K ohm pull-up.  However, just to make certain, do the circuit traces

for DQ15-DQ8 return back to the microcontroller/FPGA?  Or are these I/O's non-existent on your PC board?

Best regards,
Albert  
Cypress Semiconductor

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Anonymous
Not applicable

Hello Albert,

Yes, the packages are not  same. We are modifying the trace because of that.

DQ15-DQ8 pins are unconnected and not returning to the controller. As these are I/O pins, leaving them open might be dangerous (e.g. ESD point of view) for the IC. So, we need to pull it up/down. I was struggling with the pull-up resistor values.

Thanks for your answer!

Regards,

Saikat.

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AlbertB_56
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500 replies posted 50 likes received 250 replies posted

Hello Saikat,

A minor correction to my previous response to you. :

The actual pull-up value should be 4.7K to 10K ohm,-=and not 4.7 to 10K ohm...

Best regards,

Albert

Cypress Semiconductor

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