ESI VideoBridge 2150, Руководство по обслуживанию

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A . 2.5
Electrical Specific ations
The rela t i onship be tween the bi nary l og i c s ta tes and thei r vol tage
levels is as fol lows :
LOG I C STATE
o
I
VOLTAGE LEVEL
>
+2. 0V High is inactive s tate
<
+0. 8V Low is active s tate
The high and l ow e l ec t rica l s t a tes a r e based on s tanda r d TTL
( transis tor- t ransistor l ogic) levels where the power source does not
exceed +5. 25VDC and is referenced to logic ground.
A.2.6 Sign al Lines
The I EEE-488 bus is divided by func tion in to three separate busses as
shown in Figure A-4 : an eigh t- line da ta bus, a three- line trans fer
bus, and a five-line managemen t bus . Table A - 3 indicates the con tacts
co r responding to these l ines as we l l as t he seven signa l g r ound
returns and the bus shield.
The data bus ( signal lines D I O I through D I O 8) are used to convey
da ta o r device-dependen t messages. D I O
I
represents the leas t
significan t bit in the t ransmit ted byte; D I O 8 represen ts the mos t
significan t bit. One eigh t-bi t word can be t ransmit ted bidirec tion­
al ly in byte-serial , bit paral lel fashion. The data lines are con­
sidered active when their signal level is low.
The t ransfer bus is a three-wire handshake p rocess that is execu ted
between the talker and al l designa ted lis teners each time a by te is
transfer red over the da ta bus. This handshake process assures that
new da t a is no t p l aced on the da t a bus f as t e r than the s l owes t
l is tene r can r eceive i t . The t h r ee t r ans f e r bus l ines and thei r
functions are:
elsli
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