Tech with Dave: GO 128 enhancement for Commodore

One wonderful feature of the Commodore 128 was its compatibility with the Commodore 64. It was an evolution of the Commodore 64 and still supported all the software and hardware from before. For me it was a no-brainer to buy. 80 columns, plus new features, plus CP/M. Adding a mouse, GEOS 128, REU 512K, and 3.5" floppy, and I thought it was the best place to be this side of heaven.

There were multiple ways to go into Commodore 64 mode.

Start with a Commodore 64 cartridge
Boot/reset with the Commodore key held
Commodore 128 boot disk that switched to Commodore 64 mode
Switch MMU to Commodore 64 mode
GO 64 command

But the only way to get back into Commodore 128 BASIC 7.0 was to reset the system.

Fast forward a few decades or so, and now we can add GO commands to the other BASIC systems to switch between them. Links: cross-platform source, Windows binary release.

How does it work? This is emulation. Sorry purists. The Commodore 128 MMU was built so there is no going back out of C64 mode. This was by design to keep 64 mode on the 128 very close to 100% compatibility. But emulation? Anything goes. The GO command is hooked, the argument is checked for a number, and if the number is right, it goes to that Commodore model by restarting the emulation for that system. And thus, when running the BASIC for one system, can quickly switch to another other system (or even reset the system) using the GO command. It even prompts for amount of RAM to allocate (except 128 is fixed at 128).

PET 2001 2K to 64K supported

Vic-20 5K to 40K supported in hardware supported increments, not all available to BASIC
64 RAM 3K to 64K supported not all available to BASIC

Commodore 16 and Plus/4 support 16K, 32K, or 64K
Commodore 128 fixed at 128K (KERNAL does not do RAM test)

Limitations? Oh, sorry. This emulator is text only. No full screen editor. Doh! No screen pokes either (well not displayed). [Update 6/2021:] PETSCII and commodore graphics characters supported with third party font. Does support console history editor on Windows. Linux and MAC builds (you can build from my open source project) provide only simple line editing capability. Does provide accurate 6502/6510/8502 emulation, RAM banking, etc. according to the platform. So pop into the MONITOR on C128 or C16, Plus/4, or SUPERMON on other platforms to write and edit machine code. And because using console window, the text display size is not as limited, 88 columns for Vic-20 and 160 columns for C128.

Save and Load from .PRG is supported as well (except PET at this time, some other limitations). Disk device is ignored, so defaults to local file system. Even use absolute and relative paths.

So for simple programs, and just playing around in BASIC, it's not too bad. Text background and foreground color for Vic-20 is enabled because that color palate is more compatible with the Windows console default colors. Reverse text should work on all systems. Home, clear, cursor positioning may work in programs only, not for editing.