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From: "Frank Bemelman"
Subject: Re: Philips XA-S3
Date: Wed, 23 Oct 2002 21:47:05 +0200
X-Newsreader: Microsoft Outlook Express 6.00.2600.0000
Organization: EuroNet Internet
NNTP-Posting-Date: 23 Oct 2002 19:47:11 GMT
"Tim Kortekaas" <firstname.lastname@example.org> schreef in bericht
> I am designing a simple Philips XA-S3 dev board just for hobby purposes.
> The only thing I am confused with and that I can't find in the manual.
> Does the controller, when in 16 bit bus mode, also reads the code memory
> 16 bit?
> I myself think so, but when I look at the hex file output of the assembler
> it looks like a hex file
> for an 8 bit EPROM. A typical output looks like this:
> Anyone who can read this line immediately sees the length byte is 0x20. En
> are 32 bytes of data in the line. So this can't be a 16 bit hex file (I
> think). Or is there
> an other type of file format. Or do I interpret the output wrong. Or reads
> the XA it's
> code in bytes (not words). Or do I need to specify a compiler command in
It collects 'bytes' until a complete instruction is fetched, and the actual
number of bytes depends on the instruction. A NOP is one byte, but a FJMP
is 4 bytes, one byte for the instruction, and 3 bytes for the adress.
If you use a 16bit bus, it will fetch 2 bytes in a single read cycle. In
case, you will not be using A0 (adressline 0) since you are in fact reading
two adresses in a single read cycle. The 16bit eprom (or a pair of 8 bit
eproms) provides 2 bytes of data, for an even adress + the next odd adress.
Adressline 0 is only used with 8 bit databus. The compiler-output has no
meaning here, that is just a list of bytes, one for each adress.
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