Reserved bit in register in CY8C20234

[Tim]

I just inherited code that sets a reserved bit that does make a difference in a capsense measurement.   When the reserved bit is set I get "proper behavior" .    I did not set this bit in a test and the capsense was reading out raw data at 255 range  when it should have been reading 0.  To get this design to work this bit has to be set.   What does this bit do and how in the world could of my predecessor known to set it???? 

This bit is bit 7 in CS_CR3 that is being set by the following code segment.

CS_CR3 |= 0x90; // Reference buffer to drive the analog global bus. Bit 7 is not used so why was it set? Reserved bits should not be set. Without it the raw capsense value reads 255 instead of 0
// CS_CR3 |= 0x10; // Reference buffer to drive the analog global bus.  Causes 255 to be read in raw value instead of 0 . 

Then the capsense code below this.

[SampathS_11]

Would it be possible to try out a Code Example in your board? The Code Example I recommend to try out is for CY3280-BSM Simple Button Module Kit, which I hope can be easily modified for your board. The specific project to try out is 20x34_CSA. This project does no changes to the reserved bits. 

If possible do kindly share the schematics and PSoC Designer project for our review.

Best regards,

Sampath Selvaraj

[Tim]

I can eventually try out a code project but I have very special proprietary hardware and software so the code example would be great for learning but in no way answers my question since it also will provide no insight into reserved registers because as you stated they are not set in that example.  This question is more like a data sheet question and the question is quite clear.  The question is what does bit 7 that is reserved do in CS_CR3??  I did provide the code in the original post.  Maybe at one time this bit was documented and used.    It's very puzzling how the prior designer knew to set it to get the raw values to come out the way he wanted.    See section 10.2.4 in the attachement that talks about the CS_CR3 register but no mention of bit 7.  What does bit 7 do?

[Tim]

I can eventually try out a code project but I have very special proprietary hardware and software so the code example would be great for learning but in no way answers my question since it also will provide no insight into reserved registers because as you stated they are not set in that example.  This question is more like a data sheet question and the question is quite clear.  The question is what does bit 7 that is reserved do in CS_CR3??  I did provide the code in the original post.  Maybe at one time this bit was documented and used.    It's very puzzling how the prior designer knew to set it to get the raw values to come out the way he wanted.    See section 10.2.4 in the attachement that talks about the CS_CR3 register but no mention of bit 7.  What does bit 7 do?