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From: "Noname Nospam"
Subject: Re: Philips XA architecture design
X-Newsreader: Microsoft Outlook Express 5.00.2314.1300
NNTP-Posting-Date: Tue, 29 Oct 2002 15:29:53 EST
Organization: Prodigy Internet http://www.prodigy.com
Date: Tue, 29 Oct 2002 20:29:53 GMT
Tim Kortekaas wrote in message news:3DBD8B58.8020903@NO-SPAM.kortekaas.xs4all.nl...
> 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 MBit, 64k x 16, STMicroelectronics) it has 16
> adress lines (duh).
You have gotten a lot of general answers to your questions but to be more specific:
The M27C1024 is a 16-bit only EPROM
This means connect A1 to A17 of the XA to A0 to A16 of the M27C1024.
Connect PSEN of the XA to G of the M27C1024.
Connect E of the M27C1024 to Ground.
Connect P of the M27C1024 to Vcc.
Connect VPP of the M27C1024 to Vcc.
Verify that your EPROM programmer programs the LOW byte first of 16-bit devices.
Tim Kortekaas wrote in message news:3DBE4CE2.email@example.com...
> O.K. It's getting clearer and clearer to me.
> I think I know now how to connect a 16 bit ROM to the microcontroller.
> But now a question about the programming. When I grab the output of my
The first line from your compiler HEX output programs the first four bytes
of memory (address 0x0000 to 0x0003) with the XA reset vector.
An XA vector is made up of two words.
The first word for your code is: 0x8800 and will be loaded into the PSW of the XA.
The second word is the address of the vector handler located on page zero.
For your code this is: 0x0120
The very first thing that the XA will do after RESET is to read the reset vector.
After RESET the XA sets the bus control registers to produce the longest cycle times.
This means the XA will latch the data bus 5 clocks after the rising edge of ALE.
With your XA in external address mode (EA pin low at rising edge of reset) look 5
clocks after the rising edge of ALE to view the data on the D0 to D15.
Please note that the XA does not always produce a valid RESET vector read cycle
after RESET. It may abort this cycle but the next one will be valid.
If your code is correctly programmed into the M27C1024, D15 and D11 will both be
one and all the other data lines will be zero.
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