STD Bus

The STD Bus is a computer bus that was used primarily for industrial control systems, but has also found applications in computing. The STD Bus has also been designated as STD-80, referring to its relation to the Zilog Z80 series microprocessors. The term STD is in reference to "standard", but several marketing terms were also promulgated, including simple to design, simple to debug, and swift to deliver.

STD computer card

Description

The STD Bus uses 6.5" by 4.5" expansion card with an edge connector with 56 pins. Many different types of cards have been available for the STD Bus, from processing cards, RAM cards, I/O cards, and specialized cards for various applications.

The use of the STD bus has declined. From the over one hundred manufacturers of components during its peak, vendor numbers have dwindled to under a dozen, but it is still used by hobbyists, manufacturers and in industrial applications.

Connector pin assignments

The STD Bus has a card edge connector with 56 contacts. The pin configuration is as follows. Flow is relative using a STD Bus processor card.[1]

PinMnemonicSignal flowDescriptionPinMnemonicSignal flowDescription
1+5VInLogic power2+5VInLogic power
3GNDInLogic ground4GNDInLogic ground
5-5VInNegative logic power6-5VInNegative logic power
7D3In/outData bus8D7In/outData bus
9D2In/outData bus10D6In/outData bus
11D1In/outData bus12D5In/outData bus
13D0In/outData bus14D4In/outData bus
15A7OutAddress bus16A15OutAddresss bus
17A6OutAddresss bus18A14OutAddresss bus
19A5OutAddresss bus20A13OutAddresss bus
21A4OutAddresss bus22A12OutAddresss bus
23A3OutAddresss bus24A11OutAddresss bus
25A2OutAddresss bus26A10OutAddresss bus
27A1OutAddresss bus28A9OutAddresss bus
29A0OutAddresss bus30A8OutAddresss bus
31WROutWrite to memory or I/O32RDOutRead to memory or I/O
33IORQOutI/O address select34MEMRQOutMemory address select
35IOEXOutI/O expansion36MEMEXOutMemory expansion
37REFRESHOutRefresh timing38MCSYNCOutCPU machine cycle sync
39STATUS 1OutCPU status40STATUS 0OutCPU status
41BUSAKOutBus acknowledge42BUSRQInBus request
43INTAKOutInterrupt acknowledge44INTRQInInterrupt request
45WAITRQInWait request46NMIRQInNon-maskable interrupt
47SYSRESETOutSystem reset48PBRESETInPush button reset
49CLKOutClock from processor50CNTRLInAux timing
51PCOOutPriority chain out52PCIInPriority chain in
53AUX GNDInAux ground54AUX GNDInAux ground
55AUX +12VInAux positive56AUX -12VInAux negative

Applications

A focus of the STD bus was its ability to build a system using the exact bus cards required for an application. The compact size of a card made the STD bus system more adaptable to various applications than the contemporary computer buses of the mid-1980s such as the S-100 and the SS-50, because it could use servo control cards along with a fully programmable computer for mathematical operations.

In applications for running an astronomical observatory, the large industrial base of cards, and the system's expandability, made the system desirable for use in a photometry lab to control the telescope as well as do the data logging and computations required.[2]

In typical university laboratory settings of the mid - late 80's, STD bus data acquisition systems were commonplace using Z80 or similar processor cards for the data capture, processing and control, parallel I/O cards for experiment control as well as analogue to digital conversion cards for reading experiment analogue parameters. Such systems would only occupy minimal rack space, while providing full CP/M processing features.[3]

STD-32

The STD-32 is a pin compatible STD interface that allows the co-existence of both 8-bit and 32-bit systems on a single bus. This is accomplished by the addition of pins between the normal pins that do not connect, nor do they interfere with the original specification. This allows with the proper STD-32 backplane the ability to run legacy cards used for specific applications on the same bus without having to upgrade the complete system.

References
  1. Prolog 7801 8085A Processor Card Specifications September 1981
  2. The STD Bus and other microcomputer buses for photometrists. By Russell M. Genet and Douglass J. Sauer. From the Fairborn Observatory in Fairborn Ohio.
  3. MICRO-LEARN: A low cost microprocessor development system for laboratory use based on the STD bus, Z-80 CPU and CP/M Operating system. By D. Crosetto(INFN, Turin), Zhong-Ren Gao(Beijing, Inst. Phys.)
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