A good question at this point is why use the jump table at all? Why not just JSR directly to the KERNAL subroutine involved? The jump table is used so that if the KERNAL or BASIC is changed, your machine language programs will still work. In future operating systems the routines may have their memory locations moved around to a different position in the memory map . . . but the jump table will still work correctly!
|1)||On power-up, the KERNAL first resets the stack pointer, and clears decimal mode.|
|2)||The KERNAL then checks for the presence of an autostart ROM cartridge at location $8000 HEX (32768 decimal). If this is present, normal initialization is suspended, and control is transferred to the car- tridge code. If an autostart ROM is not present, normal system ini- tialization continues.|
|3)||Next, the KERNAL initializes all INPUT/OUTPUT devices. The serial bus is initialized. Both 6526 CIA chips are set to the proper values for keyboard scanning, and the 60-Hz timer is activated. The SID chip is cleared. The BASIC memory map is selected and the cassette motor is switched off.|
Next, the KERNAL performs a RAM test, setting the top and bottom of
memory pointers. Also, page zero is initialized, and the tape buffer
is set up.
The RAM TEST routine is a nondestructive test starting at location $0300 and working upward. Once the test has found the first non-RAM location, the top of RAM has its pointer set. The bottom of memory is always set to $0800, and the screen setup is always set at $0400.
|5)||Finally, the KERNAL performs these other activities. I/O vectors are set to default values. The indirect jump table in low memory is estab- lished. The screen is then cleared, and all screen editor variables reset. Then the indirect at $A000 is used to start BASIC.|
|This page has been created by Sami Rautiainen.|
|Read the small print.||Last updated November 15, 1998.|