Subject:
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Re: 68HC11 register locations?
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Newsgroups:
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lugnet.robotics.handyboard
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Date:
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Sat, 28 Mar 1998 16:39:20 GMT
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Original-From:
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Max Davies <mdavies@cam.orgNOSPAM>
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Viewed:
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1841 times
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Mike Vande Weghe wrote:
> I'm writing an assembly routine under IC on the
> Handy Board, but I'm
> getting a little confused about the memory
> locations of the 68HC11
> registers. The Motorola manual shows that the
> registers associated with
> the input and output timers are in the $1000
> range....
The correct actual addresses are indeed all in the
$10xx range. When you index off either the X or Y
register, the offset value is only 8 bits, or 0 to
$FF. This is why you're getting the warning
messages, the high order $1000 is being ignored.
You do not have to use the indexed method to
address the registers, these are all equivilent:
LDA #$1020
and
LDX #$1000
LDA $20,X
and
LDX #$1000
LDA $1020,X <--- gives warning, high
order $1000 ignored.
The equates allow you to use either direct or
indexed addressing to get at the registers. The
only reason for using the indexed method is to
save 1 byte on each such instruction.
/Max
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Message is in Reply To:
 | | 68HC11 register locations?
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| I'm writing an assembly routine under IC on the Handy Board, but I'm getting a little confused about the memory locations of the 68HC11 registers. The Motorola manual shows that the registers associated with the input and output timers are in the (...) (27 years ago, 27-Mar-98, to lugnet.robotics.handyboard)
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