The Expert Cartridge

The Expert was manufactured by the company Trilogic. It is a freezer cartridge, with built-in machine code monitor, but no disk turbos or other basic wedges. A unique feature of the Expert is that the software is stored in RAM, which enables simple and cheap upgrades, but also requires the cartridge to be programmed from disk before it can be used.

Scans from the cover of Trilogic's catalog. Note that the logo part of the label is upside down on the left image.

Schematics

I have reverse engineered the schematics. Since the markings on the ICs were ground off, this involved desoldering some parts and analysing them on a breadboard. (Don't try this at home.)

Postscript file

Notes

• I have (arbitrarily) numbered the ICs according to this sketch:

                 ------------
         ESM    +  U6        --
                |  U5    U     |    C64
         SWITCH +  U4    7     |    Edge
                |  U3          |  connector
         RESET  +  U2   U1   --
                 ------------
         

• The text on ICs U1 - U6 have been ground off, but the RAM, U7, has its marking left; HY6264LP-15.
• The address and data lines of the RAM are scrambled. This is probably just to simplify the layout.
• My guess is that all logic ICs (possibly with the exception of U4 and U6) are LS-TTL. This is also indicated by the fact that there is no pullup resistor on pin 13 of U3:D. This input will be left floating when the switch is not in the 'ON' position, which a bipolar TTL input can handle, but not a CMOS input.
• U4 and U6 are of the same type. My old notes suggest that they are CMOS Schmittriggers, which makes sense for those parts of U6 that are used in the delay circuits, where a high input impedance and rail-to-rail outputs are desired. It does not make sense, however, for the other gates that interface to TTL. TTL output high level is not guaranteed to satisfy CMOS input high requirements.
• All diodes are 1N4148.
• The PCB is marked 'Expert' on the top side and 'Exp.4' on the bottom.
• U5 is a quad three-state buffer. U5:B and U5:C are connected in parallel to force the NMI line high if a program leaves it low as a freeze protection.
• The label on the box says 'Patent applied for'. Does this mean the entire cartridge or just the concept of pulling the NMI line high with a strong buffer? Was the patent accepted and if so, what is it's patent number?
• Operation:

  U1:A and U1:C decode the address bus at $8000-$9FFF and $E000-$FFFF respectively. With the switch in the 'PRG' position, U3:B and U4:C enables the RAM at $8000. With the switch in the 'ON' position, U1:B enables the RAM at both $8000 and $E000, but only if the cartridge is active, that is, the flipflop formed by U3:C and U3:D is on. Writes are possible at $8000, by the help of U3:A and U2:A. (Note that the RAM won't respond to a write if the E1 input is high.)

  The U3:C-U3:D flipflop controls if the cartridge is active or not. It is switched off by I/O1, i.e. an access to $DE00-$DEFF. It is switched on by either a RESET or an NMI when the ESM LED is not lit. I have not yet figured out exactly how the ESM circuitry works.

Software

Software may come later.

Instead of using Trilogic's programming menu, I found it convenient to do a programming with the switch in its 'OFF' position, and save the memory from $8000-$9FFF to disk. Then to program the cartridge I would just put the switch at 'PRG' and load the memory image.