basically
clears
the interface to
a
known
state
appropriate to the device
being addressed. SRQ (Service Request)
is
used by
a
device to indicate the.
need for attention or
service
and
to request an interruption of data flow.
REN
(Remote Enable)
is
used to
select
between two sources of device data
(an an example: front panel or
rear
panel controls on
a
measurement device).
EOI
(End or Identify) indicates the end of
a
multiple byte transfer sequence,
or
along with the
ATN
line, executes
a
polling sequence.
3.9.2 Specific Operation of the
DRC8-IEEE
Interface
The
DRC8-IEEE
allows for the remote control of set-point, gain and
reset.
It
also provides
a
digital output of temperature in Kelvin, the
present values of set-point, gain and
reset,
as
well
as
the status of the
front panel switches and Remote/Local status.
Address and function selection
are
made
via
a
switch package located
on the
rear
panel of the
DRC
instrument
(see
Figure 3.3
DRC8-IEEE
panel lay-
out). Positions 4-8 of the switch
are
the address switches for the interface
with 4 being the most significant bit and
8
being the
least
significant bit.
As
an example: with switches
5,
6,
and 7
ON,
and switches
4
and
8
OFF, the
address selected
is
14 (or
E
base
16).
Position
3
of the switch package
is
the
TALKER
select
with position 2 being the LISTENER
select.
are
selected with both switches OFF (or up), while either
can be deselected
by turning the appropriate switch
ON
(or down).
Both functions
Switch position
1
is
used to
select
the order in which the output
delimiters are put onto the
IEEE
bus. The following table gives the deli-
miter
orientation versus switch position:
Delimiter
Order
(Delm
1)(Delm
2)
Switch
1
Position
Up
(OFF) (LF)
(CR)
Down
(ON)
(CR)
(LF)
The use of this switch allows the DRC8-IEEE to interface to controllers
which accept both forms of delimiters to terminate input strings.
NOTE:
the address switches
are
updated on power up only.
orientation
is
read only when the instrument
is
turned on. Any change in
the address switch while the instrument
is
on
will
be ignored.
The address and delimiter
The
DRC8-IEEE
transmits and
receives
all
characters in ASCII. The
cable connector
meets
IEEE-488, 1978 standards and
is
polarized for proper
cable insertion. The following table shows cable connector contact wiring
for the IEEE-488 bus:
-27-
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