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From: "Noname Nospam"
References: <3DBD8BF0.email@example.com> <firstname.lastname@example.org>
Subject: Re: Philips XA architecture design
X-Newsreader: Microsoft Outlook Express 5.00.2314.1300
NNTP-Posting-Date: Mon, 28 Oct 2002 19:09:37 EST
Organization: Prodigy Internet http://www.prodigy.com
Date: Tue, 29 Oct 2002 00:09:37 GMT
Frank Bemelman wrote in message news:email@example.com...
> "Tim Kortekaas" schreef in bericht
> > I posted a question about designing a little dev board for the Philips
> > XA architecture. But I'm still confused with something. If the processor
> > is in 16 bit mode, A0 isn't used because the processor fetches the data
> > in byte-pairs. But when I look at the specifications of a (for instance)
> > M27C1024 EPROM (1 MB, 64k x 16, STMicroelectronics) it has 16
> > adresslines (duh).
> > In my previous post (tnx for replies Frank and Paul) someone mentioned
> > the EPROM puts the data of the even and next odd adresses on the 16 bits
> > bus. But the EPROM has 64k addresses of 16bit words.
> > Do you get the confusion ?
> The processor will see the eprom as 128K adresses, each adress holding
> one single byte of information. The eprom delivers it in 2 bytes portions
> at a time, over its 16 bit databus.
> > Do I have to connect A0-15 of the EPROM to A1-A16 of the
> > microcontroller? Maybe I am making just a simple wrong step in the
> > beginning of the problem solving...
> Yes, and you will have 128 Kbytes of program memory that way.
> > And about the programming, this isn't clear to me either. The output of
> > my compiler (standard compiler from the IC25 databook CD) is in Intel
> > Hex File format. In the beginning of a line in this file stands the
> > address of the data that has to be written in the EPROM. But it are 8bit
> > numbers. Isn't every address of the EPROM filled half then?
> I think you are confused by the '16bit' aspect of this processor.
> The number of bits is not important in respect to the memory - the memory
> is a range of adresses, each adress holding 1 byte. Physically, the memory
> can have an 8 bit or 16 bit adressbus, but for the software this makes
> no difference.
It's been a long time since I did an Intel extended HEX to binary filter.
What I remember is that the HEX file will contain a record that is
used to set the "high" 16-bits of the "address space".
This record is recognized by most device programmers. Especially those
that can program devices larger that 64K bytes like the 27C1024.
At heart the XA is still an 8051. This means that each function block
of your application must fit entirely within a 64K byte memory space.
There is an errata for some XA processors that warns you when fetching
bytes from the external memory bus in 16-bit mode to end your code segment
before it grows into the last 16 bytes of the segment.
> It is similar to PC's, the pentium is 32bits, the memory-databus is
> 32bits wide, an long integer is 4 bytes, but occupies 4 adresses of
> 1 byte. If the long integers are aligned properly (and the compiler
> will do that often by default) it takes only 1 memory cycle to get
> that long integer, and it can be stuffed into the accumulator in
> one single move.
> Frank Bemelman
> (remove 'x' & .invalid when sending email)
> > I have lots experience with the 80c51 based series of Philips, but none
> > with the XA or other 16bit ucontrollers.
> > --
> > Tim Kortekaas
> > To reach me by email, remove the obvious...
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