Application Note

This document details version 02.50 of Cromemco RDOS, an operating system for the 16FDC disk controller. This new version introduces several significant improvements over previous releases, including the ability to boot from any floppy disk drive, compatibility with CDOS and Cromix operating systems (versions 11.08+ for Cromix and 02.45+ for CDOS), and enhanced flexibility in designating boot and master drives.

Key enhancements include:

• Floppy Disk Booting: RDOS 02.50 allows booting from any floppy disk, either manually or automatically via 16FDC switch settings. This provides flexibility in setting the default command drive.
• Initialization Sequence Improvement: The initialization sequence for the 1793 disk controller IC has been modified to abort operations prior to a system reset. This prevents potential data loss from runaway programs during initial disk access.
• User Entry Jump Table: The user entry jump table, used by programmers for RDOS facilities in ROM-based real-time applications, has been updated. Each entry now consists of a 3-byte Z-80 JP instruction, with the order of routines remaining the same.

The document also explains the RDOS 02.50 Boot Command, detailing its manual format (Bx, where x is an optional drive specifier) and automatic execution based on 16FDC switch settings. It outlines the messages displayed during the boot process ("Preparing to boot, ESC to abort," "Standby") and potential error messages ("No boot," "Unable to boot"). The ESC key can be used to abort the boot sequence between the "Preparing to boot" and "Standby" messages.