2031 LP CIRCUIT THEORY

Microprocessor Control of RAM and ROM

UAB4 and UAB5 are 8192 x 8 bit ROMS that store the Disk Operating System (DOS). UAB4 resides at memory locations $C000-$DFFF. UAB5 resides at memory locations $E000-$FFFF. UB7 decodes the addresses output from the microprocessor when selecting these ROMS. UB2 is a 2048 x 8 bit RAM. UB2 resides at memory locations $0000-$07FF. This memory is used for processor stack operations, general processor housekeeping, user program storage, and 4 temporary buffer areas. UA4, UB6, UB7 and UB8 decode the addresses output from the processor when selecting RAM. UB8 also controls the chip select line of the VIA, UCD4.