RadiSys 80/24A
SINGLE BOARD COMPUTER

General Description
Documents
Electronic Diagrams
Summary

General description

The RadiSys 80/24A Single Board Computer is a clone of the Intel Multibus and Multimodule compatible computer system on a single printed circuit assembly. The RadiSys 80/24A board includes an Intel 8085A-2 microprocessor, 8K bytes of on-board random access memory (RAM), sockets for up to 32K bytes of on-board read-only memory (ROM), six programmable 8-bit I/O ports, one programmable serial communications channel, a programmable interval timer, a programmable interrupt controller, and advanced bus controller.

The iSBC 80/24A board is controlled by an Intel 8085A-2 microprocessor operating at 4.84 MHz. System access is provided by the Multibus connector and an auxiliary connector. Off-board peripheral I/O operations are handled through 48 parallel lines, a serial communications channel connector and two iSBX Multimodule connectors.

The iSBC 80/24A board can directly access up to 64K bytes of memory. A single SRAM device supplies 8K bytes of on-board RAM. Also, the board can accept up to 32K bytes of user-installed ROM, PROM, or EPROM devices (either 24- or 28-pin devices). The on-board 8254 Programmable Interval Timer (PIT) provides three independent counter outputs which may be configured to a variety of applications, including frequency output, rate generator, interval timer and real-time interrupts. One of these counters serves as the baud rate clock for the on-board 8251A Programmable Communications Interface (PPI) device. Serial I/O operation is handled by an Intel 8251A Programmable Communications Interface (PCI) device. The board is configured to the RS232C structure; however, it may be adapted to a TTY interface using optional equipment. Baud rates are software programmable via the on-board timer.

The iSBC 80/24A board utilizes two Intel 8255A Programmable Peripheral Interface (PPD devices to control the six, 8-bit parallel I/O ports. These ports may be configured to a variety of dedicated or general purpose applications. Two Intel 8287 Bus Transceiver devices are supplied for two of the ports and sockets for line driver or terminator devices are provided for the other four ports.

Up to eight interrupts are controlled by the 8259A Programmable Interrupt Controller (PIC), while four additional interrupts are handled directly by the 8085A-2 CPU. An interrupt jumper matrix allows the interrupt structure to be easily configured to your application.

Two iSBX bus connectors are provided on the iSBC 80/24A board. These connectors are designed to expand the board’s I/O functions, using special purpose add-on Multimodule boards, such as the iSBX 344 Intelligent BITBUS Interface Board. One or two iSBX Multimodule boards may be added, as required by your application.
The iSBC 80/24A board is designed to operate as a full master in any Intel Multibus compatible chassis.

Electronic diagrams

The MULTIBUS System Architecture

The MULTlBUS system bus is Intel’s industry standard, IEEE 796, microcomputer bus structure. Both 8- and 16-bit single board computers are supported on the IEEE 796 structure with 24 address and 16 data lines.

In its simplest application, the system bus allows expansion of functions already contained on a single board computer (e.g., memory and digital I/O). However, the IEEE 796 bus also allows very powerful distributed processing configurations with multiple processors and intelligent slave, I/O and peripheral boards capable of solving the most demanding microcomputer applications. The MULTIBUS system bus is supported with a broad array of board level products, LSI interface components, detailed published specifications and application notes.