|Talker (extended talker)||
|Device must be able to transmit|
|Listener (Extended listener)||
|Device must receive commands and data|
|Device must properly transfer a multiline message|
|Device must properly receive remote multiline messages|
|Device must be able to operate from front panel and remote information from bus|
|Device can asynchronously request service from the controller|
|Upon controller request, device must uniquely identify itself if it requires service|
|Device can be initialized to a predetermined state|
|A device function can be initiated by the talker on the bus|
|Device can send addresses, universal commands, address commands, and conduct polls|
|This code describes the type of electrical drivers in a device|
The cabling specifications of the GP-IB interface system permit interconnecting all devices together in a star or linear configuration. The GP-IB connector is a 24-pin ribbon-type connector.
In summary, Table 2 shows the complete description of the GP-IB data bus.
8-bit parallel, monodirectional, multi-master (token passing)
One controller, one talker, several listeners
Token passing: the controller addresses the next controller
SRQ Service request when the controller assigns modes
Female connector on equipment chassis.
|Sponsor||Hewlett-Packard||Error handling||Parity bit DI07 when 7-bit ACSII characters|
|Standard||IEEE 488, IEC 625||Bus length||15 m|
|Address space||31 devices||Driver||Special 24 mA drivers|
|Data format||8-bit parallel||Speed||1 MByte/s|
|Transfer type||Write only, talker toward listener(s) or commander toward all others||Timing||
Handshaken 3-wire broadcast transfer:
DAV data valid
NDAC Not data accepted
NRFD Not ready for data
|Remarks||The 488 is most commonly used for data acquisition of H-P peripherals. Programmable interfaces and drivers exist and simplify the development of microprocessor interfaces.|
Since introduction of the IEEE-488, technology produced a generation of medium-speed, low-power, instrumentation which had a need to operate in an automatic test system such as the GP-IB. The HP-IL (Hewlett-Packard Interface Loop), was introduced to meet this need. The HP-IL is a low-cost, low-power alternative to the GP-IB system. The HP-IL and GP-IB provide the same basic functions in interfacing controllers, instruments, and peripherals, but they differ in many other respects. HP-IL is suitable for use in low-power, portable applications ( typically used for interface of battery-power systems ). The GP-IB is not practical to operate from battery power. The HP-IL maximum data rate is 20K bytes per second. This is a high rate compared to the RS-232C, but much slower than GP-IB. The HP-IL can operate over distances of up to 100 meters between any two devices. Since it is a loop environment, there is no maximum system cable restriction. The basic device-addressing scheme allows for up to 30 devices on a loop.