Bus standard for small
and medium-sized computer systems

General Description
Documentation
Examples

General description

The STD bus, introduced in the mid-1970s, represented a significant advancement in microcomputer architecture. Developed by companies such as Pro-Log and Mostek, this 8-bit bus system featured a modular backplane, allowing for the easy integration of various components.

The standardization of the bus system meant that users could seamlessly connect different peripherals and expansion cards to microcomputers, fostering compatibility and interchangeability.

While the STD bus itself did not become an IEEE standard, its adoption and popularity grew in the late 1970s and early 1980s. It became a prevalent choice for small and medium-sized computer systems due to its modular and standardized nature. This adaptability facilitated the expansion and customization of computer systems, meeting the diverse needs of users in that era.

Beyond its immediate success, the STD bus left a lasting impact on computer architecture. Its design principles influenced subsequent bus architectures, contributing to the evolution of standardized interconnectivity in the realm of microcomputers. The legacy of the STD bus can be observed in the continued emphasis on modular and standardized designs in modern computer systems.

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STD Bus Boards Examples

In my collection, I have several printed circuit boards in the STDbus standard:

Pro-Log CPU 4004 Module

This printed circuit board was developed by Pro-Log before the establishment of the STDbus standard. Nevertheless, it is very close to this standard. It is a CPU board based on the 4-bit Intel i4004 processor. The board features a clone of the i4004 processor called INS4004.

This is 4115 PRO-LOG

’CPU CARD FOR CUSTOM I/O’

includes 4004 CPU, clock, external and power-on reset and 256-word instruction PROM with capacity to 1536 words. Contains an 80-character data RAM with capacity to 320 characters. I/O bus for custom interfaces or remote I/O. Has 4 MOS output lines. Used in PLS-402.

Pro-Log CPU 8080A Module

This printed circuit board was developed by Pro-Log before the establishment of the STDbus standard.

ONE CARD 8080A / 2708 SYSTEM

Thls industry standard processor is optimized in the PLS-881 for small and medium sized dedicated control systems. I/O is expanded through multiplexing.
Includes 8080A Processor with 0.488 microsecond state time, crystal clock, single level interrupt, power-on and external reset, 1024 bytes of D1002 RAM (2102 or equivalent) and sockets for 4096 bytes of D1024 PROM (2708 or equivalent), 16 TTL input lines and 24 TTL output latches. Requires +12, +5, -5VDC. Does not include PROM.

Pro-Log CPU Z80 STD Bus Module (7803)

This card combines a buffered and fully expandable Z-80 microprocessor with onboard RAM and PROM sockets.

The 7803 includes 1K byte of RAM with sockets for up to 4K bytes and sockets for up to 8K bytes of ROM or EPROM. An STD BUS system using the 7803 card can be expanded to the full Z-80 memory and I/O capability. The 7803 STD BUS interface may be disabled for DMA and multiprocessor applications.

FEATURES

• Z-80 Processor
• 4096 bytes RAM capacity (2114)
• 1024 bytes RAM included
• 8192 bytes ROM capacity onboard (2716 EPROM)
• 3 State Address, Data, Control Bus
• Crystal controlled 400 ns clock
• Power-on reset or pushbutton reset input
• Dynamic RAM refresh control
• All IC’s socketed
• Single +5V operation
• Use Pro-Log 01004 1Kx8 memories (two 2114L’s)

Pro-Log CPU Z80 STD Bus Module (7803A)

This PCB board is a newer version of the Pro-Log 7803 module.

It combines a buffered and fully expandable Z-80 microprocessor with onboard RAM and PROM sockets.

The 7803 includes 1K byte of RAM with sockets for up to 4K bytes and sockets for up to 8K bytes of ROM or EPROM. An STD BUS system using the 7803 card can be expanded to the full Z-80 memory and I/O capability. The 7803 STD BUS interface may be disabled for DMA and multiprocessor applications.

Pro-Log CPU Z80 STD Bus Module (7880)

The 7880 provides a buffered and fully expandable 4 MHz, Z80A Microprocessor with onboard memory (ROM and/or RAM) and a 10 ms. timer. It is designed for maximum cost effectiveness and reliability.

The memory consists of sockets for 2K RAM and 4K EPROM. The memory is suitable for small dedicated control programs, or to bootstrap microprocessor systems using mass storage devices.

The timer has a fixed duration of 10ms. It is suitable as a background timer, or a debouncer for mechanical switches, and other such devices.

The 7880 allows DMA control to other cards, and is compatible with all Z80 interrupt modes.

Main Features of the 7880 are:

  • Z80A Processor
  • Crystal controlled 250 us clock
  • Socket for 2K byte wide RAM
  • Socket for 4K EPROM
  • 10 ms. timer
  • Compatible with all Z80 interrupt modes
  • DMA capability to enema! memory
  • Bootstrap capability
  • MEMEX control
  • Capable of addressing 128K bytes of memory
  • Single +5V operation

Pro-Log CPU 8085 STD Bus Module (7815)

This CPU board is an extension of the 7801 module based on the Intel 8085 processor.

Pro-Log Dual UART STD Bus Module (7304)

The 7304 provides two, fully independent, RS-232C serial data corrununication channels on a single STO card.
Asynchronous operation up to 19,200 baud is supported for full duplex OTE (Data Terminal Equipment) or DCE (Data Communications Equipment) applications.

Capabilities include a TTY Interface provision for one channel and polled interrupt logic for both channels.

Main Features of the 7304 are:

  • RS-232C Serial Interface specification
  • Dual, independent 824lA USARTs
  • Independent program selectable baud rates to 19200 baud for RS-232C
  • Independent polled interrupt logic
  • Connection available for 7320 priority interrupt card
  • Selectable DTE/DCE configuration for each channel
  • Dual 26 pin male header connectors
  • +5V, ±12V operation
  • Socketed ICs
  • ASR-33 TTY interface circuit
  • Fully comp~tible with 7801,7802, and 7803 CPU cards

Pro-Log UTILITY DIP CARD (7902)

A printed circuit card for prototyping with Dual-in-line (DIP) packaging. Accommodates 8,14,16 and 18 pin DIPs on 0.300 inch (0.76 CM) centers and 24, 28 and 40 pin DIPs on 0.600 inch (1.52 CM) centers.
Card has printed power distribution bus. Plated-thru holes accommodate 0.025 inch (0.76 CM) square posts for wrapped wire connection.

Intersil CPU Z80 STD Bus Module (ISB-3100)

The ISB-3100 is a Z80 based STD BUS microprocessor card with a 250ns clock time. The entire Z80A-CPU Instruction Set can used for programming without restiction. All signals to and from the STD BUS (address, data and control) are fully tri-state buffered. Bus arbtration logic ensures proper arbitration between on-board vs off-board memory, I/O, or interrupt acknowledge operations.

Main Features of the ISB-3100 are:

  • Full STD BUS Compatibility
  • Fully Buffered Signals for System Expandability
  • Up to 8K Bytes EPROM Capacity
  • Up to 4K Bytes Static RAM Capacity
  • Jumper Selectable (2716 or 2732 EPROMs)
  • Full Memory Decoding Capability
  • Full Bus Arbitration Circuitry
  • Four Independent Timer/Counter Channels
  • Programmable Power-on Restart
  • 4 MHz Clock Frequency
  • Internal/External Clock Selection
  • Tri-state Address, Data and Control Bus
  • Single +5V Supply
  • Optional One Wait State During Any Memory Cycle

Intersil Floppy Disk Controller STD Bus Module (ISB-3400)

The ISB-3400 is a STD BUS Floppy Disk Controller Card which can control, write to and read from up to four single or double density, single or double sided, drives.
The card will operate with Z80 based and 8085 based microprocessor cards, up to a 4 MHz clock frequency.
It is totally compatible with the ISB-3100 and the ISB-3110 Processor Cards.

Main Features of the ISB-3400 are:

  • Full STD BUS Compatibility
  • Double (MFM) or Single (FM) Density Operation – Software Selectable
  • Double or Single Sided Operation – Software Selectable
  • On-Card Direct Memory Access Controller
  • Controls Up to Four Floppy Disk Drives – 8 Inch or 5.25 Inch – Jumper Selectable
  • Compatible with IBM 3740, IBM System 34 and other Soft-Sectored Formats
  • Diskett Initialization
  • Automatic CRC Generation and Checking
  • Single-Sector, Multiple-Sector and Multiple-Track Transfer Capability
  • DMA, Interrupt-Driven, or Polled Operation
  • Digital Phase Lock Loop Data Recovery Circuit
  • Wait States – Jumper Selectable
  • Requires +5V Only