An Open Hardware Project to build a 3 in 1 Commodore 64 cartridge, based on Magic Desk 1MB and Universal c64 Cartridge by Marko Šolajić.
Due to the low cost and availability of 27c160 EPROMs nowadays, building a cartridge with 2MByte of ROM is easy to do. Furthermore, the 27c160 EPROMs can be 8 bits addressed and, given the amount of pins, being THT is an advantage.

• Magic Desk 16Kbyte config
• Double Magic Desk 1MB
• GMod3 2MB Read Only cartridge

Old Magic Desk Cartridge could be:

• Standard [32Kb (4 banks), 64Kb (8 banks) and 128Kb (16 banks)]
• DDI Magic Cart [32 banks, 256kb]
• Magic Desk Clone homebrew cart [64 banks, 512kb and 128banks, 1MB]

Furthermore:

• ROM is always mapped in at $8000-$9FFF (8k game)
• 1 register at IO1 / $DE00
  • bit 0-6 bank number
  • bit 7 EXROM (1 = cart disabled)

Magic Desk 16Kbyte config

• supports all "Magic Desk Clone" homebrew cart with 16k game config, up to 2 MB
• ROM is always mapped in at $8000-$BFFF (16k game)
• 1 register at IO1 / $DE00
  • bit 0-6 bank number
  • bit 7 EXROM (1 = cart disabled)

So, 128 banks and one bank is 16Kbyte: 2MByte of ROM space.

You can put 2 different 1MByte bin images inside 27C160 EPROM (from $000000 to $0FFFFF and from $100000 to $1FFFFF) and select them using SWCOMP1 (or JP1) switch like 2 different sides of a magnetic tape data storage.
Bin files can be made using Magic Desk Cartridge Generator, as usual.

You can configure this cartridge to partially follow the functional specifications of the GMod3 (Individual Computers) cartridge type:

• 2MB of ROM space
• ROM is always mapped in at $8000-$9FFF (8k game)
• No Write capability
• Register at IO1 / $DE00
  • bit 0-7 bank number (256 banks)
• Register at $DE08
  • bit 6 EXROM (1 = cart disabled)
• No bitbang mode

You can use the new Magic Cartridge Generator (by Žarko Živanov) to make 2Mbyte GMod3 bin images of games compilation.

All configurations

• 27C160 (DIP_42) [IC1]
• 74LS273 (or 74HCT273) (SOP_20) [IC2]
• 74LS02 (or 74HCT02) (SO_14) [IC3]
• 100nF (SMD_0805) x3 [C1, C2, C3]

Magic Desk 16Kbyte only

• 10K Ω (SMD_1206) [R3]
• 1N4148 (SMD_0805) x2 [D1, D2] (For Commodore 128 don't put R3, D1and D2, they are irrelevant)

GMod3 2MB only

• 74LS139 (or 74HCT139) (SO_14) [IC4]
• 74LS00 (or 74HCT00) (SO_14) [IC5]
• 100nF (SMD_0805) x2 [C4, C5]

Double Magic Desk 1MB only

• Push Button On Off Self Lock UnLock Switch DIP 6 Pin 7x7mm [SWCOMP1]
  • or alternatively any kind of on/off switch connected to JP1
• 10K Ω (SMD_1206) [R2]

Optional lighting eyes (all configurations)

• SMD led (SMD_0603) x2 [DE1, DE2] (UP/DOWN reverse mounted to see the light through the hole)
• From 400 to 1K Ω (SMD_1206) [R1]

Appareance

Schematics

Images

Magic Desk 16Kbyte config (Commodore 64)

JCOMP1	JCOMP2	JCOMP3	J16A1	J16B1	J16C1-8	JC64
Short 2 and 3	Short 1 and 2	Short 1 and 2	Short 2 and 3	Closed	Short 2 and 3	Short 1 and 2

(Put D1, D2 and R3)

Magic Desk 16Kbyte config (Commodore 128)

JCOMP1	JCOMP2	JCOMP3	J16A1	J16B1	J16C1-8	JC64
Short 2 and 3	Short 1 and 2	Short 1 and 2	Short 1 and 2	Open	Short 2 and 3	Short 2 and 3

(Put D1, D2 and R3)

Double Magic Desk 1MB

JCOMP1	JCOMP2	JCOMP3	J16A1	J16B1	J16C1-8	JC64
Short 1 and 2	Short 1 and 2	Short 1 and 2	Short 1 and 2	Open	Short 1 and 2	Short 1 and 2

(Put SWCOMP1 and R2)

GMod3 2MB Read Only cartridge

JCOMP1	JCOMP2	JCOMP3	J16A1	J16B1	J16C1-8	JC64
Short 2 and 3	Short 2 and 3	Short 2 and 3	Short 1 and 2	Open	Short 1 and 2	Short 1 and 2

(Put IC4, IC5, R4, R5, D3, D4, D5, D6, C4 and C5)

All configurations

JPUnlocked1
By shorting 1 and 2 it will be possible to disable and enable the cartridge using the EXROM register ($DE08 - bit 6 for GMod3, $DE00 - bit 7 for Magic Desk cartridges)
By shorting 2 and 3 it will be possible only to disable the cartridge using the EXROM register

• Žarko Živanov, for creating the Magic Desk Cartridge Generator
• Marko Šolajić, for creating some Magic Desk Clone homebrew cartridge
• Individual Computers for GMod3 specifications

If you dont want wait, can get pcb right now at PCBWay