Following is a description of some important fines on the expansion port:
Pins 1,22,A,Z are connected to the system ground.
Pin 6 is the DOT CLOCK. This is the 8.18-MHz video dot clock. All system timing is derived from this clock.
Pin 12 is the BA (BUS AVAILABLE) signal from the VIC-II chip. This line will go low 3 cycles before the VIC-II takes over the system busses, and remains low until the VIC-II is finished fetching display information.
Pin 13 is the DMA (DIRECT MEMORY ACCESS) line. When this line is pulled low, the address bus, the data bus, and the Read/Write line of the 6510 processor chip enter high-impedance state mode. This allows an external processor to take control of the system busses. This line should only be pulled low when the (&oshlash;2 clock is low. Also, since the VIC-II chip will continue to perform display DMA, the external device must conform to the VIC-II timing. (See VIC-II timing diagram.) This line is pulled up on the Commodore 64.
Reading this book and using your computer has shown you just how versatile your Commodore 64 really is. But what makes this machine even more capable of meeting your needs is the addition of peripheral equipment. Peripherals are things like DatassetteTM recorders, disk drives, printers, and modems. All these items can be added to your Commodore 64 through the various ports and sockets on the back of your machine. The thing that makes Commodore peripherals so good is the fact that our peripherals are "intelligent." That means that they don't take up valuable Random Access Memory space when they're in use. You're free to use all 64K of memory in your Commodore 64.
Another advantage of your Commodore 64 is the fact most programs you write on your Commodore 64 today will be upwardly compatible with any new Commodore computer you buy in the future. This is partially because of the qualities of the computer's Operating System (OS).
However, there is one thing that the Commodore OS can't do: make your programs compatible with a computer made by another company.
|This page has been created by Sami Rautiainen.|
|Read the small print.||Last updated November 06, 1998.|