DesTest MAX-Switch

The MAX-mode of the C64 expansion-port is truly a marvel since it allows the program on the cartridge to run right from the get-go bypassing the kernal and its assumptions about working memory.  This convenience, however, comes at a cost:  All but the bottom 4K of memory plus the kernal, BASIC and character ROMs are not available.

That's why DesTestMAX only tests 4K!  That's all it can test.

The DesTest MAX-Switch (or just the 'Switch) solution aims to fix this limitation!

The custom DesTest MAX-Switch cartridge adds the capability to switch (hence the name) between the MAX-mode and regular cartridge-mode under program control.  The new DesTest Software allows the following features:

• Full 64K memory test using the March-B algorithm.
• No dependence on the ROMs, CIAs or SID: they can be removed.
• ROM checksum verification (if installed).
• CIA TOD consistency verification.

The DesTest MAX-Switch hardware includes provisions for the following:

• Power LED.  Most of the time when diagnosing or repairing a C64, the keyboard is removed along with the Power LED.  The DesTest MAX-Switch cartridge includes a simple power LED to avoid mistakes like removing or inserting ICs with the power on.
• Reset Switch and LED.  A faulty reset-circuit in a C64 can prevent it starting-up properly.  A reset-switch can temporarily bypass a faulty reset-circuit and the LED gives a visual indication if something is wrong!

Want to see a DesTest MAX-Switch in action?  We've got you covered!  Watch these videos that feature the DesTest MAX-Switch being put through its paces.

While the DesTest MAX-Switch solution requires a specialized cartridge PCB to operate, efforts have been taken to ensure that bare circuit-boards or finalized cartridges are easily available to those that want them:

• You can buy a pre-made one from one of the vendors listed on the Where To Buy page.
• You can buy a bare PCB directly from Factor Of Matt at our Tindie store here: https://www.tindie.com/products/39331/.  These are high quality PCBs with gold-plated contacts and fit perfectly into standard short C64 cartridge cases.  The boards are priced so that buying one or two is extremely cost effective.
• You can get PCBWay to make you some of their excellent PCBs via their Shared Projects initiative here:  PCBWay DesTest Max-Switch Cartridge.  There is a minimum order when getting your PCBs made this way, but rest assured the boards can double as regular MAX-mode or EXROM carts if you don't need several 'Switches.

Building a DesTest MAX-Switch is an ideal beginner project!  The soldering is all through-hole and doesn't require anything but the most basic of skill.  The required parts are readily available and are low-cost.  The Programmable Read Only Memory (PROM) is the trickiest part of this build as there are a few different technologies to pick from (EPROM, EEPROM or Flash) and the devices needs to be programmed.

Download the DesTest MAX-Switch distribution-archive here.

While the archive does include the necessary Bill of Materials and Assembly Instructions, you may also view them at the DesTest MAX-Switch Resources page.