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+60k Introduction
by Lord Hypnos/Padua

Every coder probably once wondered how to program the C64 in "Turbo Assembler" (or another comfort editor) when using the entire RAM. The +60k is one of the possibilities to go with. The hardware is inexpensive and not too difficult to get a holdof. I am not a hardware expert and do not quite know how exactly the expansion works, but assembling it was not that difficult.

The +60k is the only expansion that comes with ready to use utilities. The +60k can only be used with the C64-II and C64-III because the old C64 is using a different chipset. You need 4 simple IC (classic logic 74LS), some conductors and one switcher (so the price comes to about 3-4 Euro) and the additional RAM. You need the same two ram ICs used in C64-II IC4464. If there's a problem located those, I'd suggest retrieving the ICs from another broken commie or from some old PC (old 286 f.e.). Maybe it is also possible to buy the RAM chips in some electronic outlet, but this is really obsolete technology.

After the installation, if the +60k is still not activated, the C64 will still use his original RAM IC. If you have turned the +60k switch to the ON position, the C64 will still use original RAM (so you will not have any problems with compatibility non +60k compliant software).

You can switch between the RAMs by changing the values in three system registers. The RAM will be switched between $1000 and $FFFF, so if you need a small routine for bank-switching, it would be best placed in $0000-$0FFF. These first 4 kbytes of RAM are not affected by the switching.

Mr. Fiz of Samar created the +60k and he also is the creator of the best utility for this expansion: "The +60k Turbo Assembler" - it is the classic "Turbo Assembler" with additional functions, debugged (compared to for example v5.1), supports illegal instructions and most importantly is adapted to the +60k.

The editor is stored from $9000 and up, the source code is stored from $1000-$8FFF. But the editor and source code are in second RAM bank, completely separated from the original RAM! So this way almost the entire RAM of the C64 can be used for storing music, graphics, etc. Due to the full integration switching from source to object is seamless (seems just like if you are using any normal version of "Turbo Assembler").

This version of "Turbo Ass" also uses the Restore key as a special key. The vector located at $0318 will go to the bank switching routine. Unfortunately this routine is stored in the dataset buffer at $033c and is lost after a reset. So I recommend to save the switching routine in some RAM position which will not be lost during a reset ($0810 for example).

The "+60k Turbo Ass" is very stable, but if you push your reset button without leaving the editor, you might not be able to run the editor anymore.

Another scener who created some utilities for the +60k is TSD of Anubis. He made a "Turbo Assembler" package, including a "Turbo Assembler" (the ill-ass cross assembler i.e.) adapted for the +60k. The editors contain a +60k menu where you can copy data between both memory banks. He also coded a few small utilities, i.e. testers for the +60k or Action Replay expansions (including the same menu as in his +60k programs), which can be used for copying and testing between banks.

So far I am only using the +60k RAM expansion and have not yet created any programs for it. I had an idea to code an IFLI editor that supports +60k, but I haven't got around to working on it so far.

In any case the +60k is really easy to you, and if you cannot get any other RAM expansion, RetroReplay or SuperCPU or do not like using any type of cross-assembler (C64 <-> C64 or PC <-> C64) setup, then this will be the right choice for you. Also you will be able to develope all your stuff on one C64!

Written by LHS/Padua
Edited by Anonym/Padua

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