1764 and C-128
Alejandro Liu
since the 1764 was identical to the 1750 REU except for ONE resistor.
Is this true? Can anybody confirm or deny this?
al...@nunki.usc.edu (Alejandro Liu)
(Simple .signature, $CHEAP$)
Joe Greco
>I heard a while back that it is possible to use the 1764 in the C-128,
>since the 1764 was identical to the 1750 REU except for ONE resistor.
>Is this true? Can anybody confirm or deny this?
The 1764 is only a 256K expander. The 1764 comes bundled with a heavy
power supply, which is really the major difference.
The 1750 is a 512K expander. The "resistor" you mention, if I recall
correctly, only involves certain versions of the 128 expanders and
early versions of the c64. Perhaps Fred B or some Commodore guru
could clear this up, I haven't had any problems running a 1750 on ANY
of my machines (even a vintage 1982 model).
I've heard of people using the 1764 on the 128, but with somewhat
limited success since a fair amount of software is expecting a 1750
(very little seems to expect a 1700). I don't have a 128, so this is
just stuff I've heard through the grapevine.
I've also heard conflicting stories about the configuration of the
1764's RAM. I know that the 1700 is two banks of 64K, and the 1750 is
two banks of 256K. I heard originally that the 1764 was two banks of
128K (!!) (rather odd) but have heard since that it is just one bank
of 256K. I know that there could be two versions of the expander out
there, has anyone seen either of these two configurations?
. JG
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Fred Bowen
>In article <24...@nunki.usc.edu> al...@nunki.usc.edu (Alejandro Liu) writes:
>>I heard a while back that it is possible to use the 1764 in the C-128,
>>since the 1764 was identical to the 1750 REU except for ONE resistor.
>>Is this true? Can anybody confirm or deny this?
>
>1764's RAM.
Officially, CBM does not recommend using the 1700/1750 expanders on a C64
nor a 1764 expander on a C128. Many people have done this and report no
problems. Using any REU on a C64 requires a beefier power supply, which is
included with the 1764.
The only difference among the REU's, aside from the amount of RAM, is a
resistor labeled R4. Its location depends upon the vintage of the board.
Its purpose is to slightly shift the timing of the dot clock in relation to
other signals on C128's. This is due to slightly different timing between
the C64 and C128 systems (TTL delays between the expansion port and VIC &
processor chips).
1700's were populated with 2 banks of 64K DRAMs, 1764's with 1 bank of 256K
DRAMs, and 1750's with 2 banks of 256K DRAMs. I was not aware of any other
configurations. A rather popular hack is increase the amount of DRAM up to
512K bytes by replacing all the DRAMs in a 1700 with 256K DRAMs (and cutting
jumper J1), or simply adding the second bank of 256K DRAMs to a 1764. Some
people who have both C64 and C128 systems install a switch and 390 ohm resistor
at location R4, so that they can switch in the resistor for a C128 and switch
it out for a C64. Usual disclaimer- these hacks void your warranty and are
done entirely at your own risk.
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Geoffrey Welsh
> From: al...@sal43.usc.edu (Alejandro Liu)
> Message-ID: <24...@nunki.usc.edu>
> I heard a while back that it is possible to use the 1764 in the C-128,
> since the 1764 was identical to the 1750 REU except for ONE resistor.
> Is this true? Can anybody confirm or deny this?
Aside of that, they're functionally identical.
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Geoffrey Welsh
> From: jgr...@csd4.milw.wisc.edu (Joe Greco)
> Message-ID: <5...@csd4.milw.wisc.edu>
>
> I've heard of people using the 1764 on the 128, but with somewhat
> limited success since a fair amount of software is expecting a 1750
> (very little seems to expect a 1700).
controller reads. There is only one bit to indicate the size of RAM, and most
128 programs test it rather than do a RAM limit test. The 1700 (128K) had the
bit cleared, the 1750 (512K) had it set. The 1764 (256K) has it set.
I know the folks at CBM are 'listening', so I won't give a detailed opinion
on the intelligence of that design decision.
> I've also heard conflicting stories about the configuration of the
> two banks of 256K. I heard originally that the 1764 was two banks of
> 128K (!!) (rather odd) but have heard since that it is just one bank
> of 256K. I know that there could be two versions of the expander out
> there, has anyone seen either of these two configurations?
soldered another 8 RAM chips to bring the cartridge to 512K) but, from a
software point of view, ALL the RAM expanders have 64K banks (allowing 16-bit
addressing within the bank).
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Mary Ann Fall
fact, GEOS 128 directly recognizes the 1764 as a RAM 1541. However, the only
other program I've found that works with the 1764 in 128 mode is the public
domain program REUtility. In 64 mode, however, the 1764 does just fine. But
since I have such limited use for it in 128, I have the REU plugged into an
expansion cartridge where I can switch it on or off instead of unplugging
it. As I understand it, the only difference between the 1764 and the 1750
is the resistor and eight chips. In fact, I know of at least one person (and
have heard of others) who have installed the eight chips and effectively
turned their 1764 into a 1750--an option I'm considering if the chips can
be found in these chip-famished days.