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65816 in 1541 [message #210371] Thu, 24 October 2013 11:50 Go to next message
Anonymous
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Originally posted by: pcuser

Commodore 1541 has 6502 processor. What if it is replaced with 65816 ? 1541 goes faster? what is the result??? I am curious...
Re: 65816 in 1541 [message #210372 is a reply to message #210371] Thu, 24 October 2013 16:43 Go to previous messageGo to next message
Payton Byrd is currently offline  Payton Byrd
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On Thursday, October 24, 2013 10:50:19 AM UTC-5, pcuser wrote:
> Commodore 1541 has 6502 processor. What if it is replaced with 65816 ? 1541 goes faster? what is the result??? I am curious...

You actually need the 6508 processor. Next, you would need to change the clock to get any perceptible speed boost. Finally, you need to write custom drive software to use the 16-bit code.

Now, if you max out the RAM with the 6508 CPU you could conceivably write 16-bit code to run on the drive as a coprocessor to the CBM machine attached to it. You could even theoretically chain multiple such devices together and use a CBM machine to act as a traffic cop. This would be similar to the Apple Crate project.
Re: 65816 in 1541 [message #210374 is a reply to message #210371] Thu, 24 October 2013 23:45 Go to previous messageGo to next message
Anton Treuenfels is currently offline  Anton Treuenfels
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"pcuser" <pcuser4@yahoo.com> wrote in message
news:6d1e0ef7-239c-45b8-80fb-e87006f68143@googlegroups.com...
> Commodore 1541 has 6502 processor. What if it is replaced with 65816 ?
> 1541 goes faster? what is the result??? I am curious...

Disregarding the different pinouts of the two processors and assuming you
could just drop in a 65816 (a 65802 might be a better choice, but it hasn't
been available for quite some time), not much would happen. The 1541 ROM
would still be using only 6502 instructions, so none of the native 65816
instructions would apply. The 1541 clock speed would not change, so the ROM
code would not execute faster except for those 6502 instructions which are a
cycle or so faster in the 65816.

Nor would the data transfer rate to a C64 or C128 change. The 1541 can
already transfer data between its own internal RAM and a floppy diskette at
50K/sec. The limiting factor is the 0.4K/sec software serial transfer
protocol between the computer and the drive. Just changing the 1541's
processor won't change that..

It would be possible to execute programs loaded into the 1541's internal RAM
using the full 65816 instruction set. That sort of thing is most commonly
used to substitute a different software serial transfer protocol for the
built-in one, upping the drive to computer transfer speed to 2K/sec or so.
But as that can already be done with the existing 6502, there would have to
be a really compelling alternative use at hand to make it worthwhile putting
in a 65816.
Re: 65816 in 1541 [message #210377 is a reply to message #210371] Fri, 25 October 2013 07:19 Go to previous message
J.B. Wood is currently offline  J.B. Wood
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On 10/24/2013 11:50 AM, pcuser wrote:
> Commodore 1541 has 6502 processor. What if it is replaced with 65816
> ? 1541 goes faster? what is the result??? I am curious...
>
Just a general comment: For those of us like myself who like to keep
ancient CBM stuff maintained and operating to original factory specs I
wouldn't even think of trying it. However, I have applied
CBM-manufactured 1541 drive ROM upgrades (primarily to have GEOS work
correctly with two early model 1541 disk drives). I still have some
Compute!/Compute's Gazette magazine ads that show a modified 1541 with
LED status indicators at the top. Never saw such an animal in
operation, though. There were some 1541 internal RAM expansion and
spindle speed control upgrades from the folks who made the Maverick copy
utilities that would allow entire disk tracks to be written at once.

All I require is for these devices to work as intended by CBM. They're
not meant to substitute for items available 30 years later. Sincerely,

--
J. B. Wood e-mail: arl_123234@hotmail.com
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