Indus GT C64 Floppy Disk Drive Tech Info


This is just an info dump of pictures / data that I've reverse-engineered for the Indus GT floppy disk drive for the Commodore-64.  Almost every other tech page that you'll find if you Google "Indus GT" will bring up hits for the ATARI 8-bit version of the Indus disk drive, a completely different beast!  If the tech info you find mentions a Z80 CPU being built-in, that's the Atari disk drive they're talking about.

A brief ROM disassembly and tech info (also a couple D64s of the Indus "ROM-Disk")

Click on any picture below for a larger version.

Indus GT Drive Memory Map 7-Segment LED bit mapping Contents of the "ROM Disk" in U19
Photo and PCB chip layout of the Indus GT main board Photo and PCB chip layout of the Indus GT upper drive board

Misc. Textual Information:

The Indus ROMs (1.1 is what I have) in U17 and U18 are very similar to the C= 1541 ROMs, except for several changes here and there to deal with checksums, the LED displays, and the ROMDisk. RAM and I/O locations seem to be identical to the 1541 to maintain compatibility.

ROM U19 is a ROM unique to the IndusGT and is mapped in from $A000-$BFFF. The locations in the U17-U18 ROM that patch in extra functionality often jump to some new routines in U19.

The "Track", "Drive", and "Error" buttons can be read from $1201 in the I/O space; and I imagine that the "Protect" button (and drive # switches) is mapped through the VIAs.

The U19 ROM has a byte-to-Hex routine for displaying data on the 7-segment LEDs, and what looks like an unused test routine that displays the current stack size on the display.

The ROMDisk is interesting, of course. The disk loading routine returns hardcoded "invalid sectors" if drive #1 is selected but any track other than #18 is requested. The ROMDisk has its directory in track #18, and all the programs are also located in track #18. I have done some hacking to U19 to put my own small programs on the ROMDisk, and it works, but the sector values have to be put in manually and the "ROMDisk image" assembled by hand (or in a script).

LED Error Codes:

if the flat ribbon cable (J2) on the drive mechanism is disconnected (this doesn't always produce an error) or if the brown J3 connector on the drive mechanism is disconnected
if there is a fault with RAM
if ROM U19 has a checksum error
if ROM U18 has a checksum error
if ROM U17 has a checksum error
If any other chips are malfunctioning or removed in the main PCB, the LED display is unpredictable.  (Merits further investigation.)

Upon power-up, the 7-segment LEDs show "88", then "--", then the drive tests zeropage RAM, the three ROM checksums, then finally RAM $100-$7FF integrity. If these tests pass, my drive LEDs show " 1" and the BUSY light turns off.


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