FLOW Control
When
transmitting data using modems to interconnect
two devices via the telephone lines, the normal handshak-
ing
lines
are
not used.
The
two devices
can
still communi-
cate using a data-transmission technique called "flow
control." Using this method, the data sent
can
be
separated from non-data
being
received (such
as
noise).
This
is
done
by
interpreting every correctly framed data
pattern
as
a valid character
and
constantly checking for
two specific characters that turn the transmission
on
and
off.
These flow-control characters
are
called
XON
(transmis-
sion
on)
and
XOFF
(transmission off).
The
usual assign-
ment for these
is
<control-O>
for
XON
and
<control-S>
for
XOFF,
though the specific characters chosen
are
a
function of the communications program used.
When
com-
municating over telepnone
lines,
flow control greatly
increases the chance that ASCII or
HEX
encoded data will
be
correctly transferred.
The
FLOW
ON
command allows the oscilloscope some
on/off control of the data transfer. At power-on, the default
data encoding
is
BINARY. Flow control
can
not
be
used
for the transmission of binary-encoded waveform data, so
the power-on setting of
FLOW
is
set to off. Before sending
binary-encoded data, FLOW
OFF
must
be
sent if flow con-
trol was previously set
ON.
The
Advanced Functions
menu
-
___,
of the 2230 also has a
menu
choice for setting
flow control.
Remote-Local Operating States
The
following paragraphs describe the two operating
states of the instrument: Local
and
Remote.
REMOTE OFF
(LOCAL)-With
REMOTE
OFF,
instrument settings
are
controlled manually
by
the
operator using the front-panel controls. Option interface
messages
such
as
REMOTE
ON,
ROS
ON,
and
OPC
ON
are
received
and
executed. Queries about instrument's
states or measurement results will
be
answered. Device-
dependent commands that require
an
instrument operating
mode
change to
be
made
cause
an
execution error,
and
a
service request will
be
generated if
ROS
is
on.
REMOTE
ON
(REMOTE)-ln
this state, the
oscilloscope executes
all
commands sent to it. Remote-
controllable front-panel indicators
and
CRT readouts
are
updated
as
commands
are
carried out. There
is
no
local
lockout
(LLO).
Changing
any
option-controllable front-panel
setting locally overrides the remote settings. If a waveform
Options
and
Accessories-2230 Operators
is
being
transmitted, the PLOT indicator will
be
lit,
and
new waveform data will not
be
acquired until the
transmission
is
done.
Reset Under Communication Option Control
Certain default settings for acquisition
and
plot modes
may
be
set
up
sending the INlt command.
The
INlt com-
mand does not invoke the power-up test. Upon completion
of the INlt command,
no
status byte or event code
is
generated.
The
default settings
are
as
follows:
ACQUISITION REP:AVE
ACQUISITION HSREC:SAMPLE
ACQUISITION LSREC:PEAKDET
ACQUISITION SCAN:PEAKDET
ACQUISITION ROLL:PEAKDET
ACQUISITION SMOOTH:ON
ACQUISITION WEIGHT:4
(16
in
the 2220
and
2221)
ACQUISITION NUMSWEEPS:0
ACQUISITION VECTORS:ON
DATA ENCDG:BINARY
DATA SOURCE:ACQ
DATA TARGET:REF1
(REF4
in
the 2220
and
2221)
PLOT GRAT:OFF
PLOT FORMAT:<power-on setting>
READOUT
ON
Menu
system reset.
RS-232-C PROGRAMMING
Things to consider
when
writing programs for your
RS-232-C controller
are
given
here
to
help
you
when
you
must develop your own interfacing software. Before a pro-
gram
can
be
used
to control the oscilloscope, the
RS-232-C communication parameters for
baud
rate,
line
terminator,
and
parity must
be
set. Settings for these
parameters
are
selected
and
set using the RS-232-C
PARAMETERS switch found
on
the
side
panel
of the
oscilloscope.
Controller programs
are
usually composed of two main
parts or routines.
The
two parts
are
generally called the
command handler
and
the service-request handler.
7-15
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