Processor addressing modes

Scarfacé · 16 Oct 2010 at 17:45

Hey guys,

I know this isn't software as such, but I thought it would the best subforum to ask - any help would be much appreciated. I need to select a small microprocessor to copy a programme from ROM to RAM and then execute it - the programme will read from an input port, then use the data to index in to an array of constant values and then write the data retrieved from the array to an output port.

Does anyone know which addressing modes would be needed to do this? I've been reading a lot with regards to the different types of addressing modes but I'm still not confident which modes I will need. I know I'm going to need some kind of indexing addressing mode to handle the array but I'm not sure which one?

Thanks for any help.

NickK · 18 Oct 2010 at 07:40

I'm assuming this is x86?

Xelene · 18 Oct 2010 at 09:22

How big is the dataset?

Scarfacé · 18 Oct 2010 at 17:16

The two microprocessors I have been considering are the Z80 and the 6502 (narrowed down from a list of four that I can use).

The input/output data is 8 bits wide and the addresses are 16 bits wide.

After lots of Googling, I'm thinking:

To jump – Immediate Addressing
To copy ROM to RAM - Direct Addressing
Reading from Input Port - Direct Addressing
Index into array of constant values - Index addressing
Write the data retrieved from the array to an output port - Register indirect addressing

I've done quite a bit of high level programming before but I've rarely worked with assembler so as you can imagine, I'm struggling with this quite a bit...!

Cheers guys.

Chaos · 18 Oct 2010 at 18:31

Theres a load of assembler books on world of spectrum which uses the z80, might be worth a look.

http://www.worldofspectrum.org/books.html

You could run this emulator and have a play.

http://zxspectrumdev.blogspot.com/2009/01/setting-up-development-environment-on.html

Xelene · 18 Oct 2010 at 19:03

The Z80 is a nice CPU. It's been 20 years since I wrote any code for it, so cant help much

NickK · 18 Oct 2010 at 19:19

I used to code for the 65C02 in assembler

It's not really a nice chip for 16bit addressing.. actually I don't think it can do 16bit without doing hardware paging.. but last time I touched it was about 20+ years ago..

If you can - have a look at thumb ARM (very easy assembler, far better than any out there). Also Blackfin 5xx series is worth a look although the assembler is a nightmare.