ESI VideoBridge 2150, Service Manual

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A . 2 . 2 GPIB Bus S tructure and Supported Inter face Fun ctions
The IEEE-488 bus is a se t of s i xteen signal l i nes that can be grouped
func t i onal l y into three specif ical ly dedica ted buses.
1. 8 bidi rec t i onal data l i nes --
010
1 through DIO 8.
2. 3 interface signal l i nes -- DAV, NRFD, and NDAC
3. 5 general managemen t l i nes -- ATN, EOI, IFC, REN, and SRQ.
Informa t i on i s t ransferred along the bus in bi t-paral lel, byte-serial
fash i on by an asynchronous handshake. The handshake signals
( inter­
face signals DAV, NRFD, NDAC ) guarantee the t ransfe r of each byte of
data f rom an addressed talker to al l addressed l is teners. Th i s al lows
ins t ruments w i th di fferent data t ransfer rates to operate together on
the bus as l ong as they conf o r m t o the handshak e s t a te d i agrams
def i ned i n the IEEE s tandard.
Ins t ruments connec ted to the bus are classif ied as ei ther talkers,
l is teners, or con t rol lers. A tal ker is capable of t ransm i t t i ng data
on the data l ines; there can be only one tal ker a t a t ime to avoid
confusi on in message and data t ransfer. A l istener is capable of
respondi ng to da ta received on the data l i nes ; there can be more than
one l is tener a t a t ime. A con t rol ler designates wh i ch dev i ces are to
tal k or l isten and exerci se o ther bus managemen t func t i ons. There can
be a sys tem con t ro l l e r as w e l l as o t her con t ro l l ers on t he bus.
However , there can be onl y one con t rol ler- i n-charge at a t ime.
A devi ce need not always be a tal ker or l is tener or con t rol ler, i t
may be idle par t of the t ime. An i nst rument may al ternate as a tal ker
and a l i s tene r depend i ng on whe the r i t i s gene r a t i ng da t a o r
receiving ins t ruc t i ons. Figure A-4 i s a typ i cal system based on the
IEEE-488 bus st ructure.
Table A-2 l is ts the IEEE-488 In terface Funct i on reper toi re i ncluding
the subsets of each funct ion suppor ted by the VideoBr idge. The ANSI/
IEEE s tandard descr ibes these func t ions i n more deta i l.
e l s l i
A - II
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