Rainbow Motherboard

This document contains a comprehensive set of 23 circuit diagrams detailing the architecture of a "Rainbow Motherboard." The schematics cover various subsystems, starting with the Power Supply Unit (PSU), watchdog timer, and reset logic. It outlines the master clock generation and division for the system's 8088 and Z80 CPUs, as well as video components.

Key sections illustrate the distinct interfaces for both the 8088 and Z80 processors, including address/data bus management, memory access (ROM for BIOS, DRAM for main memory), complex RAM timing, arbitration between the CPUs for memory access, and refresh control logic. A significant portion of the document is dedicated to the video system, detailing master timing, video address generation, video RAM, character generation, video shift register, and analog video output circuitry.

Peripheral control is thoroughly documented, encompassing I/O port decoding, serial and printer ports with their respective baud rate generators, keyboard interface, floppy disk controller, and non-volatile RAM (NVRAM). The document concludes with diagrams for expansion bus connectors, providing interfaces for additional memory and peripherals.