MEMORY ORGANISATION The only I/O firmware that remains active when INTIOROM is turned on is the 80- column display driver. When INTIOROM remains inactive, i.e. INTIOROM = 0, the possible I/O activities are: • parallel printer • serial printer • RS232 • 80-column text • mouse • 1 M RAM expansion • FDD (Floppy Disk Drive) controller (5.2573.5") At any one time, only one kind of printer can be used (either parallel or serial). This is selected by a switch on the front panel of the computer. 3.2.3.2 I/O firmware control a) INTIOROM = 1 If INTIOROM equals one, all the internal ROM area ($C100 to SCFFF) can be accessed freely.
b) INTIOROM = 0 If 80ROM is reset, then the internal $C3XX (for 80-column) and its expansion ROM cannot be accessed. Should 80ROM be active, the 80-column firmware can be accessed. 3-5