xpSimpleBUS - A Simple BUS System eXPerience

Home didactic, I/O oriented, simple 8-bit BUS-system.

Contents

• system containing the schematics and pcb of the xpSimpleBUS system backplane and activity-monitor hardware.
• device containing the schematics and pcb of the xpSimpleBUS devices hardware.
• bridge containing the schematics and pcb of the xpSimpleBUS bridges hardware to interface xpSimpleBUS to a CPU or other BUS systems.
• interface-rpi containing the software and hardware resources to interface xpSimpleBUS to RaspberryPI.
• interface-pic16f6x8 containing the software and hardware resources to interface xpSimpleBUS to PIC16F6x8.
• expresspcb containing the schematic and pcb components used for drawing the layout of xpSimpleBUS boards.

Specifications

BUS

• Power lines :
  • +5V
  • Gnd
• Address lines :
  • A0-A7 - 8-bit Address
• Data lines :
  • D0-D7 - 8-bit Data
• Control lines :
  • /RD - Read Operation line. "Lo" value indicates the device is being read by the CPU.
  • /WR - Write Operation line. "Lo" value indicates the device is being written by the CPU.

I/O Address Mapping

Addresses	Assignment
n8H-nFH n=[0,F]	Available
n0H-n7H n=[0,F]	I/O Device (AL-config)

Basic System Operations

System operations are signal based sequence of commands, directed to DEVICEs connected to the xpSimpleBUS, and generated by an external CPU (i.e. connected to the BUS directly or through a bridge board).

WRITE OPERATION

1. CPU writes and latches Address on BUS
2. CPU sets Control Line /WR
3. CPU writes Data on BUS
4. CPU unsets Control Line /WR
5. DEVICE latches Data from BUS

READ OPERATION

1. CPU writes and latches Address on BUS
2. CPU sets Control Line /RD
3. DEVICE writes Data on BUS
4. CPU reads Data from BUS
5. CPU unsets Control Line /RD
6. DEVICE releases BUS

Schematics and PCB

• Schematics and PCB layouts are designed with ExpressPCB free CAD software.

Boards

System Boards

• simplebus-backplane-4 - backplane with 4+1 slots.
• simplebus-bus-expansion - 2-slot bus expansion.
• simplebus-activity-monitor - test board for bus pins activity.

Bridge Boards

The Bridge boards are designed to interface the xpSimpleBUS system to a CPU or other kind of BUS systems.

• simplebus-bridge-admux - bridge board to connect the xpSimpleBUS to an external BUS with multiplexed address and data lines.

Device Boards

I/O Device Boards

In order not to increase the complexity and size of the i/o pcbs, only the address pins A₀A₁A₂A₃ are scanned to enable the device, with pin A₃ always high. Then the device responds also to addresses n0H-n7H, with n in 0..F.

• simplebus-device-input-port - 8-bit input port with selectable address (by a 8-jumper row) in a range of 00H-07H.
• simplebus-device-output-port - 8-bit latched output port with selectable address (by a 8-jumper row) in a range of 00H-07H.

RAM Device Boards

• simplebus-device-sram-128bytes - 128x8-Bytes Static RAM.

Future Plans

• Add more xpSimpleBUS boards and specs
• Implement xpSimpleBUS based projects

About & License

Author: Alessandro Fraschetti (gom9000).
License: This experience is licensed under the MIT License. The license applies to all the documentation, schematic files, and PCB layouts provided in this repository.