IEEE-488

IEC -625 bus is the international standard name for an external parallel data bus, which is used primarily for connection of measuring devices and peripherals such as plotters and printers to a computer, with up to 15 devices can be connected. The maximum speed of the standard is 1 MByte / s

Other names

History

The bus was in the 1960s by Hewlett -Packard (HP) developed as HP -IB, and filed by the latter in the 1970s to IEEE standards. In 1975, the standardization as IEEE -488 -1975. 1978, the standard was revised and as IEEE -488 published in 1978 (later renamed IEEE 488.1, IEEE 2004 renamed to 60488.1:2004 ). HP -IB conforms to this standard. ANSI adopted the standard as ANSI Standard MC 1.1. The IEC took over the standard as IEC 625th

In 1987, the IEEE adopted a supplement, IEEE 488.2 (also known as IEEE 60488.2:2004 ), which extends the original standard, not replaced. The original standard defined, no data transmission protocols or device commands. In order to curb the proliferation of manufacturer solutions, 1990 IEEE 488.2 standard was extended by the SCPI command language. Many devices meet even today not the IEEE488.2 standard.

Faster variations are known, for example as HS488, which was standardized in 2003 as IEEE 488.1-2003. However, older devices are sometimes not able to process the HS488 protocol. In a mixed configuration therefore has to be taken into account.

Basic structure

The bus is a parallel 8 -bit bus, which can be connected up to 15 units. Although 30 devices can be addressed, however, the physical specification allows only the connection of 15 devices per bus. The bus 16 includes signal lines, eight data lines, three for the control of data transfer ( handshake ), and five signals to the bus management.

Each connected device must be assigned manually once one of the 30 possible addresses. Classically, takes place on the device with a DIP switch. Some devices also allow to set the address in the device's firmware.

From the connected devices may at one time send a maximum of one data ( the device that was previously defined as a talker ), but the data for several of the other connected devices can be sent, as all non-transmitting devices are allowed to read from the bus at the same time (actually must actively reading devices are previously defined as listener).

Through a 3 -phase handshake ( Ready / Data valid / data accepted) determines the slowest device on the bus, the speed of transmission. Therefore, it is inconvenient to mix devices with significantly different rates on a bus, unless the loss in speed can be tolerated.

The standard defines several logical functions of devices ( eg Source Handshake (SH ), Acceptor Handshake (AH), Service Request ( SR ), or Control ( C), with a trailing digit indicates the implemented ( sub) functionality ( 0 = no effect.) on devices or in manuals these " skills " (capabilities ) are the interface specified in the aggregate, eg " SH1 AH1 T6 L4 RL1 SHR0 PP0 DC1 DT 0 C0 ". , the bus requires, in contrast to standards such as Universal Serial bus (USB ) is not necessarily a controller. Thus, for example, a set on talk only instrument to be connected directly to a printer set to listen only for logging.

Only IEEE 488 1 defines the transmission of data is not the command for controlling peripheral devices. This requires an additional protocol is required, for example, HP uses a protocol names CS -80 ( Command Set 80) for its own periphery.

Bus signals

Connectors

IEEE -488

IEEE -488 uses 24 -pin Centronics connector (official name: " Micro Ribbon Connector" ), often realized as plug - socket combination at both cable ends. The complete bus is looped through these combinations to the bush. There can then in turn be bolted an identical connector. The connectors are thus " stackable ", where the number of successive mated connectors for mechanical reasons is usually limited to 4. To fix the connector exist in both metric ( M3.5 × 0.6 ) and inch retaining screws that do not match with each other. By convention, the (now mostly encountered ) metric variant is black, the contrast inch silver running. In practice, this system also allows a flexible bus cabling. Both a star and a linearly arranged cabling is also possible hybrid forms are permitted.

\            | --- \            | ---     DIO1 | 1 13 | DIO5     DIO2 | 2 14 | DIO6     DIO3 | 3 15 | DIO7     DIO4 | 4 16 | DIO8     EOI | 5 17 | REN     DAV | 6 18 | GND (twisted with DAV)     NRFD | 7 19 | GND (twisted with NRFD )     NDAC | 8 20 | GND (twisted with NDAC )     IFC | 9 21 | GND (twisted with IFC)     SRQ | 10 22 | GND (twisted with SRQ)     ATN | 11 23 | GND (twisted with ATN )     SHIELD | 12 24 | Signal GND            | ---            | --- /            / IEC -625

The IEC -625 bus uses a 25-pin D -sub connector. This variant was introduced by the IEC standard and could be against the established 24 -pin connector according to IEEE -488 on the market not prevail.

Platinum plug connection

Commodore introduced the plug connection on the computer often made ​​as a cost, but impractical due to the lack of strain relief platinum plug connection. This is evidence that a 24 -pin standard connector via ribbon cable can be connected directly:

Platinum platinum notch notch 1 - DIO1 9 - IFC E - REN         | | 2 - DIO2 10 - SRQ F - GND                               1 1 1 3 - DIO3 11 - ATN H - GND    1 2 3 4 5 6 7 8 9 0 1 2 4 - DIO4 12 - GND J GND -    5 ============ - EOI A - DIO5 K - GND   # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # 6 - DAV B - DIO6 L - GND    ============ 7 - NRFD C - DIO7 M - GND    ABCDEFHJKLMN 8 - NDAC D - DIO8 N - GND DIN connectors according to DIN 41524

Also of Commodore there was a proprietary serial version of the bus under the name CBM bus, were used in the circular DIN connectors according to DIN 41524.

Application

The bus is still widely used today in laboratories for the management and control of measuring instruments. However, it is not limited to this use, it is a general purpose ( for general purposes intended ) bus, which served for a long time as a standard connection for plotters and printers. Also, mass storage, floppy disk drives, using tape drives to hard drives were connected via IEEE -488, for example, for HP workstations of the 1970s and 1980s.

The Commodore PET / CBM had this bus also and used it mainly for floppy disk drives and printers. The later Commodore 8 -bit models from VC -20 to C128 used the proprietary serial version of CBM - bus.

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