ESI VideoBridge 2150, Руководство по обслуживанию

Страница: 276 / 332

The gr oup of signal lines used t o con t r ol the orderly flow of inf or­
rna ti on across the IEEE-488 da ta bus is ca lIed the managemen t bus.
These signal 1 i nes perf o rm such impor tan t tasks as de tec t i ng i n ter­
rupts, set ting a device to remo te contr ol, and announc i ng the end of a
message. The f i ve management bus signals are:
ATN (At tention)
specif y how da t a
The con t r oller-i n-cha rge uses th i s
on t he bus a r e t o be in t e r p re t ed.
signal t o
I t also
specif ies which devices along the bus mus t respond t o the data.
When ATN is set low, the data bus will convey addressed commands,
un i ve rsal commands, listen addresses (MLA), talk addresses (MTA),
o r secondary addresses. The codes co r r esponding t o these commands
and addresses are defined in Appendix E of the IEEE-488 standard.
S RQ (Servi ce Request) The con t roller-in-charge receives this
signal se t l ow by a device reques t i ng se rvice. The c o n t r oller
c o nduc t s a p oll t o de t e rm i ne which device o n the da t a bus
activa ted the inter rupt. The con t roller can take the app r op riate
ac tion by branch ing to an interrupt service routine.
EOI (End O r Ident ify) -- The EOI line is set low t o indicate the
end of a mUltiple byte t ransfer sequence. The con t r olle r- i n-charge
execu t es a parallel p oll i ng sequence when the EOI and the ATN
lines are set low simultaneously. The VideoBridge does n o t suppo r t
the parallel polling mode.
IFC (Interface Clear) -- The system con t r oller sets this signal
low t o initialize the interface func t i ons of all devices connected
t o the da ta bus, i. e. , set them t o an inactive s ta te, then re turn
con t r ol to the sys tem con t roller.
REN (Remo te Enable) -- The sys tem con t roller sets this line low t o
activate the remo te mode, disabling f r on t panels of ins t rumen ts on
the bus. This management line is no t suppo r ted by the V i deoBridge,
so i ts state will be ignored.
elsli
A - 17
2150/2160 5/85