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Date: Wed, 30 Oct 2002 13:38:17 +0100
From: Tim Kortekaas
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Subject: Re: Philips XA architecture design
References: <3DBD8B58.8020903@NO-SPAM.kortekaas.xs4all.nl> <5dCv9.2205$B72.email@example.com>
Noname Nospam wrote:
> 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.firstname.lastname@example.org...
>>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.
IDEA: I don't need such a big ROM (of 1 megabit). Can I just program the
code above in 2 8bit EPROMs of 8kb. If I connect A1 to A12 of the XA
to A1-A12 of the 2 EPROMS. A0 of the first ROM to ground and A0 of the
second ROM to Vcc. Then D0-D7 of the first ROM to D0-D7 of the XA and
D0-D7 of the second ROM to D8-D15 of the XA. Will this work?
I guess I can't program the above code in a 16bit ROM without
preprocessing the HEX file to adjust it to fit in a 16bit ROM...
To reach me by email, remove the obvious...
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