Tektronix 2221 - QUESTIONS AND ANSWERS

行
Appendix
B -
2221
Operators
C
C
QUESTIONS AND ANSWERS
C
П
Here are
answers to
some
typical
questions that
you
may have about operation of the Communications
Options .
Q : Why does the data transfer rate slow down at 4800
baud ?
П
Q :
What
is the
data
transfer rate ?
CCC
A : For the
Option
10
GPIB
interface , the data
transfer
rate is
approximately
1
Kbyte per
second
.
This
equates to one waveform per second for 1 k records
or about four
seconds
for 4
K
waveform
records
.
A : At that baud rate , the internal data buffer of the 2200
Family oscilloscope fills before the oscilloscope's
processor is ready . That interrupts the processor from
its other tasks , and it must stop to issue flow control
commands to
halt
further
data
input
while
it
gets
ready to accept the data from the buffer . After it
handles the buffer data , it must then start the data
input again . All the interrupt handling slows down the
transfer
rate
.
At
2400
baud
,
the
oscilloscope's
processor is usually ready to handle the incoming data
before
the buffer
fills
,
and
it
is
not
necessary
to
continually
interrupt the data
flow .
For the
Option 12 RS - 232
- C
interface
,
the data
transfer rate
depends
on
the
format (
ASCII , HEX ,
or
BINARY
)
and the baud
rate .
Typical times for
1200 ,
2400
,
and
4800
baud are
given
in
Table
B
- 2 .
m
П
1
Q : The operators manual states that multiple commands
may be sent in one message line , but sometimes
errors are generated when I try this with Option 12 .
Why is that , and what can I do about it ?
Table B - 2
RS - 232 - C
Transfer
Rates
A : To answer the second question first , write RS - 232 - C
controller
programs
to send only
one
command at
a
time
.
Baud
Rate
Record
Size
Transter
Time
( Min : Sec )
Format
1200 4K
ASCII
HEX
BINARY
2:20
1:10
0:36
For the
first
question
of
why
multiple
commands
sometimes
cause
errors
, the
answer
is that
only one
command
at
a time can be
reliably
handled
by the
processor . Commands ( and arguments to commands )
are
interpreted and
handled
as
they are
recognized
;
the oscilloscope processor does not wait for the
message terminator to end the message . If a service
request is generated by one of the commands in a
command
string ,
correcting action may have to be
taken
. If
the
service
request is not
handled
properly
,
all following commands in a string may not be valid ,
and the
controller program may not be able to
continue .
1K
ASCII
HEX
BINARY
0:36
0:20
0:10
2400
n
П n
7
1
4K
ASCII
HEX
1:15
0:40
0:20
BINARY
1K
ASCII
HEX
BINARY
0:19
0:10
0:05
Q :
Sometimes
when
I send
commands to
change the
operating state of the instrument , they are not
accepted . What is the problem ?
4800 4K
ASCII
HEX
BINARY
2:39
1:16
0:45
A : The REM
ON
command must be
sent as the first
command
before
attempting
to
change the
operating
state of
the
oscilloscope . The
power
- on
state of
REM
is
OFF
.
IK
П
ASCII
HEX
BINARY
0:58
0:29
0:13
Q :
When
I
send
waveforms to
the
oscilloscope
at
2400
baud or more , i get bad transfers when I try to use
binary -
encoded
curve data
. What is the
problem
?
了
月
B - 17