Set up – exactly what do nick-select bits represent and just how will they affect overall memory addresses? – stack overflow
The concept is there are some designs where you might want to do not have the memory answer for each transaction.
One situation is perhaps you can possess a memory with say 8 items of address, that does not limit you to definitely 256 addressable products if you’re able to put greater number of these chips around the board. Put two chips around the board wire the low 8 address bits as much as both, the information lines as much as both, however a small amount of logic (an easy inverter really) may be used to have address bit 8 either enable nick select on among the chips or another. and address bits 7.. then decide which item within that memory. Address bit 8 as being a would enable nick select on among the recollections although not another and address bit 8 as being a 1 throughout the transaction would assert nick select alternatively memory although not the very first.
Another scenario is consider a 32 bit wide bus using 8 bit wide parts. If you wish to perform a 32 bit write then you need to assert nick select on all of the recollections. the address line is associated with these in the same manner but byte lane bits -7 take presctiption one memory, byte lane 1 bits 8-15 take presctiption another memory and so forth. If the transaction around the bus informs you it is really an 8 bit transaction which is on byte lane then you definitely only assert nick select on byte lane for your transaction. 16 bit lower byte lanes then only chips selects for that lower two recollections are asserted another two aren’t. only individuals two recollections can get written others not. usually there’s an indication on the wider bus (say 32 bit) that may do byte sized writes, one common strategy is a byte lane mask of some kind, four separate control signals that are asserted when the byte lane can be used and never otherwise employed for that transaction you are able to directly or with an inverter tie individuals towards the nick select from the memory.
The concept is there are some designs where you might want to do not have the memory answer for each transaction.
One situation is perhaps you can possess a memory with say 8 items of address, that does not limit you to definitely 256 addressable products if you’re able to put greater number of these chips around the board. Put two chips around the board wire the low 8 address bits as much as both, the information lines as much as both, however a small amount of logic (an easy inverter really) may be used to have address bit 8 either enable nick select on among the chips or another. and address bits 7.. then decide which item within that memory. Address bit 8 as being a would enable nick select on among the recollections although not another and address bit 8 as being a 1 throughout the transaction would assert nick select alternatively memory although not the very first.
Another scenario is consider a 32 bit wide bus using 8 bit wide parts. If you wish to perform a 32 bit write then you need to assert nick select on all of the recollections. the address line is associated with these in the same manner but byte lane bits -7 take presctiption one memory, byte lane 1 bits 8-15 take presctiption another memory and so forth. If the transaction around the bus informs you it is really an 8 bit transaction which is on byte lane then you definitely only assert nick select on byte lane for your transaction. 16 bit lower byte lanes then only chips selects for that lower two recollections are asserted another two aren’t. only individuals two recollections can get written others not. usually there’s an indication on the wider bus (say 32 bit) that may do byte sized writes, one common strategy is a byte lane mask of some kind, four separate control signals that are asserted when the byte lane can be used and never otherwise employed for that transaction you are able to directly or with an inverter tie individuals towards the nick select from the memory.
nick select is just an enable. the rest of the signals are overlooked if nick select isn’t asserted, so that you can see there are numerous ways this can be. For many designs if you just tie nick select to ground (if it’s asserted low) after which it always gives creedence to another signals.
Quantity of nick selects makes no difference. you might have 32 bit wide recollections having a single nick select for your memory you might have a gigabit part (recollections are often spec’ed in bits not bytes the width is really a separate a part of that spec) or perhaps a 4 gigabit part 32 bits wide you have 4 occasions the memory. might have 8 bit wide parts with increased memory than the usual 32 bit wide part. usually one nick select per part/module but may that varies too. there’s no direct link between quantity of nick selects and just how much or how wide the memory is, a minimum of in this point in time, within the day’s the z80 and 8088 and the like you didnt possess a wide variety of 16 bit or wider parts, thus the whole reason for the 8088 was to obtain their 16 bit processor have the ability to make use of the 8 bit wide parts generally available.
Resourse: https://stackoverflow.com/questions/55520849/
