don’t care bits

17:01 May 9, 2017 

What you describe here looks like wildcard bits (don't care/X/quelconque), not bits "sans effet".

16:54 May 9, 2017 

When an adress bus comprises N bits out of which only M are used for address decoding the N-M are called don't care bits, as shows the document below:

Address decoders invariably decode regions that
start on an address that is a power-of-two. The
decoded region is invariably also a power-of-two.
Therefore the address range can be written as a bit
pattern that the decoder responds to. For example,
a decoder for addresses from 2 0000H to 2 7FFFH
( , 32 kBytes) would respond to addresses of
the form 0010 0XXX XXXX XXXX XXXX where
the X’s are “don’t cares.”

http://www.ece.ubc.ca/~edc/464/lectures/lec8.pdf

16:44 May 9, 2017 

In that case, Alain, the writer of the original text has misused the term "don't care" bits, it would seem, as "don't care" bits have a very specific meaning, as I have documented. This is something the translator ought to report back to the client and check. If indeed these are not real "don't care" bits, then "sans effet" would be correct, and ideally, the client should correct the confusing source.

16:38 May 9, 2017 

This has nothing to do with networking hardware but with address decoding.

"In partial address decoding, not all address lines in the address bus are used in the decoding process. Figure 127 shows two memory devices configured using partial decoding, where A23 is used to distinguish between the two. In this example, M1 and M2 are repeated 2,048 times through the memory space. When A23=0, M1 is selcted; when A23=1, M2 is selected."

http://users.cecs.anu.edu.au/~Matthew.James/engn3213-2002/no...

16:27 May 9, 2017 

http://etherealmind.com/basics-what-is-ternary-content-addre... :

"A Ternary CAM (TCAM) stores 0, 1, and “don’t care”. The “Don’t Care” at an additional cost over binary CAM since the internal memory cell must now encode three possible states. This is usually implemented by adding a mask bit (“care” or “don’t care” bit) to every memory cell. An access-list is a common function that uses TCAM (ternary content addressable memory) to have the flexibility to match on various layers of a packets L2-L4 headers. That TCAM memory has the ability to match (0), not match(1) (the binary is counterintuitive there) or not care (wildcard)."

16:24 May 9, 2017 

Some translators here confuse the very specific meaning of this "don't care" bit with "no effect" or "negligible", purely based on a linguistic, but flawed interpretation (at least they provide no technical documentation for their claim that this bit is negligible), apparently without looking up in the many technical descriptions of this bit on the Internet. I have provided links to technical descriptions that clearly explain the meaning and use of this bit. It has nothing to do with unused bits. When we translate technical terms, we need to ensure the technical meaning is preserved. A superficial linguistic translation is not enough.

The link just posted by Alain Boulé is not about this special type of chip with a "don't care" bit at all.

16:21 May 9, 2017 

Linear Decoding :

In small system hardware for the decoding logic can be eliminated by using only required number of addressing lines (not all). Other lines are simple ignored. This technique is referred as linear decoding or partial decoding. Control signals BHE and Ao are used to enable odd and even memory banks, respectively. Figure shows the addressing of 16K RAM (6264) with linear decoding.

https://www.allsyllabus.com/aj/note/EEE/8086 Microprocessor ...

11:29 May 9, 2017 

Bits négligeables