WORKSHOP - CIA-IDE - IDE interface for C64/128

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Introduction

I always wanted to have a harddrive in my C64 and then in my C128. First, in 1998 when I just started my adventure with electronics (adventure with programming 6502 started 4 years earlier :), a friend sent me documents about connecting ancient PC MFM harddisk controller to C64. Unfortunately I've never seen any disk like that. About a year later when I finally had access to the Internet I used search engines to find something about connecting harddisk to an 8-bit computer. There were many projects, and I slowly started to examine them one by one.

Most of them worked flawlessly on C64, but all of them failed on C128. I don't know why, maybe it is slightly different bus timing or something like that (IDE bus is not 100% compatible with C64/128 address/data bus). Anyway I admitted failure and resigned from high performance transfer in favour of reliability. I returned to the very first project I have found - driving IDE bus with additional port chip. In C64/128 case the easiest and fastest way is to connect additional CIA chip, that is CIA#3.

Building

Building that interface is very simple. For a C128 you need only CIA 6526 and some wires, C64 version needs additional TTL chip unless you will use I/O1 or I/O2 signals from cartridge port, but that might cause problems with extra hardware on the cartridge port.

You should better download the archive below and read CIA-IDE.txt file, but here is a better looking version of schematic. Grab PDF here. PDF has better quality than the image below.

/CIA3 signal comes from the address decoder. Resistors and LED are optional (in fact I don't have them in my circuit). I'm not sure if LED orientation on the schematic is correct :)

Address Decoder

This is required for C64 and might be needed for C128. An address decoder is just additional IC that will split I/O address space into smaller pieces. VIC is visible in $d000-$d3ff area but everything above $d03f is just a mirror of the first 64 registers. Similarily, SID is accessible in $d400-$d7ff area but has only 32 registers. You can take over that address space and split it into 8 smaller pieces, each one of 256 bytes.

These numbers (chips and pins) are only for C64! Get VIC (U7) chip out of the socket and bend pin 10 up. Do the same with SID (U9) and its pin 8. Connect two wires to those bended pins. Connect also another two wires to the corresponding pins on the board - in sockets. You may try to trace the tracks and find more comfortable place to solder. If not then the solder side of the board will be the safest choice.

These numbers (chips and pins) are only for C128! VIC is U21, its /CS signal is on pin 13. Instead of soldering to the VIC socket you may use U11 pin 42 - this is the very same signal. SID is U6, its /CS signal is on pin 8, board side signal can be found on U3 pin 15. The rest is similar to C64.

When you'll get those 4 signals connect them as on the picture below:

/CS lines are on those bent pins and A8/A9 lines can be taken from CPU (U6) pins 15 and 16 (respectively). On C128 you should better use A8/A9 from one of ROMs or Expansion Port because of MMU interference.

Don't forget to connect power (VCC to pin 16 and GND to pin 8) for the new chip!

As you see you get 5 I/O page signals - for $D100, $D200, $D300, $D500, $D600 and $D700. Pages $D5, $D6 or $D7 are generally a good place for connecting second SID - you just solder one SID on another, without pins 1-4 and 8. Then you solder two capacitors to pins 1-2 and 3-4 and /CS line from our address decoder to pin 8. If you want to have a stereo SID then don't solder pins 27 together and build a copy of amplifier from the board. You might also not solder pins 23 and 24 because these are POTX and POTY and might be used to mesaure resistance.

Instead of SID and VIC you could also use CIA#1 and CIA#2, but these are usually not socketed. /CS signal in CIA is on pin 23. This way you would get slices of 64 bytes each - 4 on page $DC00 and 4 on page $DD00.

Choose one of /Dx00 lines and use it as /CIA3 signal.

Download

Use local copy of archive (25.07.2002) for latest documents and program sources. You will find there comprehensive information about CIA-IDE, other possible hardware solutions and working examples of software, together with full source code of GEOS driver and installer.

Here are prebuilt binaries or GEOS driver (25.07.2002). These are ready for use with GEOS64+IDE64 or GEOS128+CIAIDE.

Here is updated IDE64 driver (11.09.2004). It works with VICE 1.15 IDE64 emulation and comes in two versions - for master and slave device, thus it should be possible to have master disk for IDE64 native stuff and slave only for GEOS.

Software

Even the best hardware is nothing without the software. I built this interface mostly for use with GEOS, and so GEOS driver for both GEOS64 and GEOS128 v2.0 is included (you can find it at address above). It is built-in into an auto-executable installer/configure program. For the first time you must run it manually, from DeskTop, after configuring and formatting the disk it will be enough to put it on the boot floppy so it will be seen right after Configure program.

Due to memory problems the driver needs RAM expansion on a bare C64. It can be either REU or internal RAM of IDE64 interface.

Source code for all utilities is available under GNU GPL license, so if you have already an IDE interface you can easily adapt it.

As for now only Master disk on the IDE bus is supported.

Usage

The configuration program will try to determine the size of disk and divide it into 16MB partitions. Note that these partitions are not the ones known from PC. All data on the disk will be lost. Each partition will be seen from GEOS as a separate disk, but you can't have currently two partitions as two different devices under GEOS. Always only one is active. There is a DeskAccessory that can switch partitions at any time.

Read the docs for more details.

Because of my laziness I have only 8-bit interface so half of disk is always lost, but even taking 20MB from a 40MB drive is a lot of space for use.

Notes

There are other similar projects. If you want a complete solution you should buy CMD drives (rather expensive) or less expensive IDE64 interface. For cheap but very compatible solution try IECATA.

Photos

Here are some photos of my setup. Click to enlarge.

General view of my C128 interiors with everything installed. On the bottom left you can see circuits for 256KB expansion and address decoder. On the top left there is Conner 40MB hard disk. As you see it is powered by C128 power supply. It worked without any problems with WD 2500MB disk.

Now similar view to previous one, but with disk removed.

Closeup of the third CIA. As you see the chip socket is soldered directly to CIA1 and a short IDE cable leads to the IDE socket.

This is actually not CIAIDE, but IECATA assembled by me. It is not finished, the IDE socket is not soldered. The axe is for size comparison ;).

Important note for IDE64 users Filesystem provided by this GEOS driver is not compatible with IDE64 native filesystem. This means that you can't share the disk between the two and you can't copy data without intermediate medium (like a floppy). Use it with care, but remember that only master disk is supported by my software, so it should be possible to have to drives - master for GEOS and slave for IDE64.

Anyway I think you will find this auto-exec for IDE64 useful. It is a little program that you should put on your boot disk. Every time you start GEOS it will read the time from RTC onboard IDE64 and set the system time and date.

Last words

Please contact me if you build this interface. I would like to hear your comments, answer to your questions, maybe solve your problems or fix bugs in software.