A92: Treznor

To: assembly-92@lists.ticalc.org
Subject: A92: Treznor
From: Hmlacage@aol.com
Date: Tue, 5 Aug 1997 15:04:57 -0400 (EDT)
Reply-To: assembly-92@lists.ticalc.org
i am currently rewriting the file for newbies.txt: it will be released as
soon as possible...
here is the part u told was too complex: i hope it is a little more clear: i
doubt i can make it more simple... 
question: have u understood without pbs the part which is up to this ? 
thanks for answering, mathieu, <hm lacage@aol.com>


Your calc is made of 2 parts:
      *** The memory: where the data is stored under a binary form. "Data"
          means the instructions with their parameters which are to be
          executed by the processor. This mem is the RAM ( 128 kb on most
          calcs ) and the ROM ( 1 Mb on all 92 ) 


      *** The processor, the heart of the calc: 2parts

       a) a small part of memory in the processor where parameters for the
       near to come instructions are stored: the registers...
       b) the processor itself, where instructions are executed...

The registers are some small micro switches which can be set to anything we
want: we use to store the data we want to process in these regs. We may put
there numbers to add or adresses to data ... ANYTHING !
Registers are a small memory which is physically in the processor. This very
small memory is VERY IMPORTANT: it is used store vital info on the state of
the processor and some info you need

These registers have been created because acessing to the memory is slow:
if the data is very near to where it is to be processed , the speed is
greatly increased. Registers are very usefull because they allow a very
flexible programming...
There are five sorts of regs:

a) Dataregisters: numbered from 0 to 7 ( there are 8 ) : D0/D7  : 32 bits
b) adressregisters: A0/A6  : 32 bits
These are for you: you may store in these registers all data you wish.
you may store in these registers 32 bit data

c) A7 : stack register ( it is phisicaly similar to A0/A6 but it is used in
a totaly different manner and you should not meddle with it ... )  :32 bits

d) Status register:  16 bits
composed of 2 bytes: the lower byte, the flag register is widely used:its
bits are set depending on the result of some operations executed by the
processor. ( see jimmy mardel ' s guide : 68k programming for more details
or wait some days till i get to the instructions part ) the upper byte,
the system byte is a group of bits used by the system: you can use them too
but it requires to know what you are doing which is not my case yet.

e) program counter: 24 bits 
the program counter is a register in which the adress in memory to the next
instuction to be executed is stored : you cannot modify its content !