Technical Notes
Four switches on the 4FDC interface card are used to set the operation of the card. Switch 1 is the RDOS DISABLE switch. When this switch is ON the 1K ROM containing RDOS cannot be accessed by the computer. When this switch is OFF the RDOS program resides in the computer memory space from address 0xC000 to 0xC3FF.
Switch 2 is the RDOS DISABLE AFTER BOOT switch. If this switch is ON the 1K ROM containing RDOS will automatically be disabled after CDOS is bootstrapped in from a disk thus clearing memory space from 0xC000 to 0xC3FF for system use. (In this mode the ROM is actually disabled by an output to port 40H which is done automatically by CDOS). If switch 2 is OFF, RDOS remains in memory space even after CDOS is loaded.
RDOS contains two programs; 1) the CDOS bootstrap program and 2) the console monitor program. Switch 3 is the BOOT ENABLE switch. When this switch is ON the bootstrap program will execute (thus loading CDOS) without first entering the monitor program. If this switch is off, RDOS begins in the console monitor mode permitting the bootstrap operation or other operations to be performed under console control.
Switch 4 is the INITIALIZATION INHIBIT switch. When this switch is ON, diskettes cannot be initialized under software control thus preventing a "runaway," program from unintentionally altering the diskette initialization. This switch must be OFF when initializing diskettes.
Read more about this topic: 4FDC Floppy Disk Controller
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