Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

A0 bit of the microprocessor not connected to A0 of flash

Status
Not open for further replies.

ece4afe

Junior Member level 1
Joined
Jun 16, 2005
Messages
15
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,281
Activity points
1,422
Hello,

I am working on a project using a 16 bit mcu which is being connected to a 16 bit wide Flash Memory. I just want to know the reason behind why is the A0 bit of the microcontroller does not usually connect to A0 of the Flash memory (or some other types of memory device). A1 of the mcu is usually being connected to A0 of the external memory devices like the flash, which I am using right now.

Please give me some advise.

Regards,

Chris
 

Re: A0 bit of the microprocessor not connected to A0 of flas

What memory and microprocessor? Maybe the processor can access either at byte level or at word level. The A0 can be controlled by some glue logic depending on the access type - byte or word, and of the convention little/big endian. If I remember corectly, for 8086 there were signals like BHE - bus high enable to select word access, lower byte or higher byte . Also it depends on the instruction format.
36_1176416705.jpg
 

The usual reason for this is to simplify the address generation in the microcontroller. The FLASH probably only output full 16 bit words. Therefore, if you "throw away" A0 on the microcontroller, you do not have to worry about odd addresses and byte boundaries.
The first location of in the flash is at address 0x0000 and also at address 0x0001 from the perspective of the microcontroller. Discarding A0 means any computed address doe not need to checked for its byte boundary. If the computed adddress is odd, you automatically round down, when dropping A0.

On systems that deal with only 32 bit words, we often drop off the last two bits of the address bus for the same reason.
 

Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top