Commodore SX-64 Portable Computer

The Commodore SX-64 Restoration Blog.

The Commodore SX-64 has the same basic design as the Commodore 64, but incorporates the monitor and a floppy diskette drive into a single chassis. The electronics are spread across three circuit boards in the chassis making service a challenge.

Design Notes:

CPU Board

There are three EPROMs/PROMs on the board

1. UD1, Character Generator ROM, P/N C 901225-01, 0x?000-0x?FFF

2. UD3, Kernal ROM, P/N C 251104-04, 0xE000-0xFFFF

3. UD4, BASIC ROM, P/N C 901226-01, 0xA000-0xBFFF

When the 6510 CPU is powered on and the 555 timer lets go of the RES\ line, the CPU loads the PC from the address stored at 0xFFFC, and then starts executing instructions at 0xFCE2. The CPU disables interrupts, configures the stack, and checks for an autostart=cartridge.  If it finds an autostart=cartridge it loads the PC from the contents of 0x8000 and runs the software in the cartridge. If an autostart=cartridge is not found, it configures the I/O chips, scans for RAM, enables interrupts, then loads the PC with 0xA000 and executes the software in the BASIC ROM.