| Author |
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Computer Architecture Stu
Guest
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 Posted:
Sat Oct 22, 2005 4:15 pm Post subject:
Programming using IAS instruction set |
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Hi guys!
IAS instructions DON'T include any indirect addressing mode like LOAD
M(M(X)). As most of you already know that in order to come up with a
counter controlled loop, we really need indirect addressing mode. If
the only addressing mode in IAS is direct mode, then how can we come up
with a controlled loop?
Thank you inadvance. |
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Joe Seigh
Guest
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| Posted:
Sat Oct 22, 2005 4:15 pm Post subject:
Re: Programming using IAS instruction set |
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Computer Architecture Student wrote:
| Quote: | Hi guys!
IAS instructions DON'T include any indirect addressing mode like LOAD
M(M(X)). As most of you already know that in order to come up with a
counter controlled loop, we really need indirect addressing mode. If
the only addressing mode in IAS is direct mode, then how can we come up
with a controlled loop?
Thank you inadvance.
You can always add the base and index register together in a third |
register and use that to address your data. Right?
--
Joe Seigh
When you get lemons, you make lemonade.
When you get hardware, you make software. |
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John Mashey
Guest
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| Posted:
Sun Oct 23, 2005 12:15 am Post subject:
Re: Programming using IAS instruction set |
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Joe Seigh wrote:
| Quote: | Computer Architecture Student wrote:
Hi guys!
IAS instructions DON'T include any indirect addressing mode like LOAD
M(M(X)). As most of you already know that in order to come up with a
counter controlled loop, we really need indirect addressing mode. If
the only addressing mode in IAS is direct mode, then how can we come up
with a controlled loop?
Thank you inadvance.
You can always add the base and index register together in a third
register and use that to address your data. Right?
|
Wrong.
IAS machines, like others of that era, didn't have base or index
registers, jsut a couple accumulators that did not participate in
address formation. The only addressing was an n-bit memory address
contained in an instruction.
People did array programming by modifying the instructions. In some
cases, there were special instructions that stored the low-order n-bits
of an accumulator into the address bits of an instruction.
The Manchester Mark I is usually credited as the first to have index
registers; see http://en.wikipedia.org/wiki/Index_register.
Note: ofthe IAS-derived machines, I think the only one left is RAND's
Johnniac, happily preserved from the dumpster (but only by the greatest
of luck) at the Computer History Museum, wwew.computerhistory.org |
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Rob Warnock
Guest
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| Posted:
Mon Oct 24, 2005 2:36 pm Post subject:
Re: Programming using IAS instruction set |
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John Mashey <old_systems_guy@yahoo.com> wrote:
+---------------
| People did array programming by modifying the instructions. In some
| cases, there were special instructions that stored the low-order n-bits
| of an accumulator into the address bits of an instruction.
+---------------
Like the "R" & "Y" instructions of an LGP-30, to cite another case
of a machine with no base or index registers. "R" was specialized
for storing subroutine return addresses into the return jumps, and
"Y" [store AC<addr_field> ==> mem<addr_field>] was used for general
computed addresses, such as array addressing.
-Rob
-----
Rob Warnock <rpw3@rpw3.org>
627 26th Avenue <URL:http://rpw3.org/>
San Mateo, CA 94403 (650)572-2607 |
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John Savard
Guest
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| Posted:
Mon Oct 31, 2005 1:15 am Post subject:
Re: Programming using IAS instruction set |
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On 22 Oct 2005 06:00:38 -0700, "Computer Architecture Student"
<nivine.dalleh@gmail.com> wrote, in part:
| Quote: | IAS instructions DON'T include any indirect addressing mode like LOAD
M(M(X)). As most of you already know that in order to come up with a
counter controlled loop, we really need indirect addressing mode. If
the only addressing mode in IAS is direct mode, then how can we come up
with a controlled loop?
|
You use self-modifying code, if you don't have index registers.
Don't these youngsters nowadays know _anything_?
John Savard
http://home.ecn.ab.ca/~jsavard/index.html
http://www.quadibloc.com/index.html
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