| Many times it would be
beneficial to capture and store a waveform (or
continuously changing DC voltage) to be viewed or
analyzed later, either by the test program or the
operator. A digital storage oscilloscope (DSO)
can accomplish this very easy. With the FT-100
controlling the scope through the RS-232 port,
waveforms may be downloaded and analyzed as
needed. The only problem with this scenario is
that most DSO's are relatively expensive and
aren't always available when needed.
This application
note describes a simple FT-100 software routine
that may be used to capture a waveform and
optionally store it on disk. The waveform is
stored in an ASCII format that is recognized by
most graphing, spreadsheet, and data analysis
programs. Once captured, the waveform can be
analyzed by the FT-100 just as easily. This
routine is very flexible and can be easily
modified for each given application.
The FT-100 could
never compete with a high-speed DSO, but for some
limited applications, the ability to store and
analyze a waveform, coupled with all the other
features of the FT-100, gives you a very
inexpensive method of data analysis. For many
tasks, a high-priced DSO cannot be justified, but
the ability to record a waveform could make the
test job a lot easier and more thorough.
Possible
Applications
- Low frequency
audio analysis.
- DC pulse-width measurements.
- RC time-constants - This could be used to
roughly read a capacitor or resistor value.
- Waveform comparisons.
- Power supply rise and fall time.
- Low-frequency distortion analysis.
- Switch "bounce" characteristics.
- "Peak" voltage measurements.
Features
- 12-bit analog
input.
- Any expansion module analog input line may be
used for the waveform input.
- Triggering may be from any of the following
sources:
Analog input
line (trigger voltage may be set).
Digital
input line (can be any digital input line,
including those in the main unit).
Trigger
polarity may be positive or negative (for analog
or digital trigger inputs).
- Number of samples recorded may be specified,
and is limited only by the amount of available
memory in the FT-100. (The routine
indicates the available memory.)
- Time between each sample is programmable.
- Waveform may be stored on a floppy disk. Data
is stored in ASCII format that is readable by
most data analysis programs and
spreadsheets.
- Waveform may be stored in an array for analysis
by the FT-100 program.
- Normally, several thousand data points can be
stored (up to over 60,000!).
Limitations
Because the FT-100
was not designed specifically to be a digital
oscilloscope, there are some limitations that you
must keep in mind before, and during,
implementation of this routine:
- Only analog I/O
Expansion Modules may be used for the waveform
input. The main unit cannot
be used.
- The smallest sample speed allowed is 42 msec. per sample.
- The time between each sample is always in
increments of around 2.8 msec.
- During waveform recording, the FT-100 cannot
perform other tasks.
How the
Waveform Capture Routine Works
The real work is
done inside the assembly subroutine to maximize
speed and efficiency. When keying in the assembly
routine data statements, be very careful!
It is very easy to key in an incorrect data
number. After the program loads in the assembly
subroutine, the parameters for the waveform
capture routine are set. Your particular
application will most likely determine how and
when these parameters should be set. The
parameter information is passed to the assembly
routine by placing the information in a given
section of RAM (through POKE commands). After all
the parameter information is placed in RAM, the
assembly subroutine can be "called" at
any time. The assembly subroutine stores the
waveform in memory and returns to the main
program.
After the waveform
data has been stored in memory, it can then be
stored to a disk file, sent out the serial port,
or saved in an array for processing and analysis
within the FT-100. In order to save the
information in an array, place the following set
of commands after the SYS command that
calls the assembly subroutine (Note: If an array
is used to store the data, it must be dimensioned
at the beginning of the program.):
BEG_ADDR=DATA_SEG*16
'Address in RAM of the
beginning of the data
S1 = F_SCALE/((1+(RES*15))*256):S2 =
REF*(F_SCALE/2) 'Voltage scaler multipliers
FOR X=0 TO (SAMPLES-1)
A(X) = S1 *
(PEEK(I+BEG_ADDR)+PEEK(I+BEG_ADDR+1)*256) - S2
INC I : NEXT
There are several
commands that calculate and process information
to be placed in the FT-100 operating system.
These appear confusing, and probably don't make
much sense, but they are necessary for the
assembly routine to operate most efficiently.
When keying in
this program, the comments may be omitted as you
see fit. They are there only to help clarify the
program operation.
WAVE_1
'Program Name
PROG_LEN= 170
'Number of bytes in assembly program
'
'--- Test for enough memory to load in assembly
routine ---
LAB_BEG=PEEK 45+(PEEK
46*256)+((PEEK 47+(PEEK 48*256))*16)
STR_BEG=PEEK 59+(PEEK
60*256)+((PEEK 61+(PEEK 62*256))*16)
MEM_FREE = LAB_BEG -
STR_BEG-16
'Total
available memory
IF PROG_LEN>MEM_FREE
THEN BEEP:CLS:DISP:DISP
"INSUFFICIENT":DISP
"MEMORY!":END
'
MEM_DATA = MEM_FREE -
PROG_LEN 'Memory available for data storage
'
'--- Read in assembly routine & store in
memory ---
PROG_SEG=INT
(STR_BEG/16)+1:PROG_OFF=0
ADDR=PROG_SEG*16
FOR X=0 TO PROG_LEN:READ
D:POKE (X+ADDR),D:NEXT 'Load assembly program
'
'----------------- Assembly Program DATA
statements ----------------------
DATA
1EH,2BH,0D2H,8EH,0DAH,0BEH,74H,1
DATA
0FFH,34H,46H,46H,8BH,0CH,46H,46H
DATA
8BH,1CH,46H,46H,8AH,14H,46H,8BH
DATA
2CH,46H,46H,8AH,24H,46H,8BH,3CH
DATA
8EH,0DFH,2BH,0FFH,5EH,8AH,0C7H,0EEH
DATA
0B0H,1EH,0FEH,0C8H,75H,0FCH,0F6H,0C3H
DATA
1,75H,29H,0F6H,0C3H,2,75H,45H
DATA
0E8H,11H,0,89H,5,0E2H,2,1FH
DATA
0CBH,47H,47H,8BH,0C6H,2DH,1,0
DATA
75H,0FBH,0EBH,0ECH,8AH,0C7H,0EEH,42H
DATA
0B0H,10,2CH,1,75H,0FCH,0ECH,8AH
DATA
0E0H,4AH,0ECH,0C3H,51H,0E8H,0ECH,0FFH
DATA
8BH,0C8H,0E8H,0E7H,0FFH,0F6H,0C3H,80H
DATA
74H,0BH,3BH,0C5H,73H,0F2H,2BH,0E9H
DATA
73H,0EEH,59H,0EBH,0C6H,3BH,0C5H,76H
DATA
0E7H,3BH,0CDH,0EBH,0F3H,51H,52H,8AH
DATA
0D4H,8AH,0CCH,80H,0E1H,7,0B4H,1
DATA
0D2H,0E4H,0B1H,4,0D2H,0EAH,0ECH,22H
DATA
0C4H,8AH,0E8H,0ECH,22H,0C4H,3AH,0C5H
DATA
74H,0F9H,8AH,0E8H,0F6H,0C3H,80H,75H
DATA
2,32H,0C4H,3CH,0,75H,0ECH,5AH
DATA 59H,0EBH,8DH
'-----------------------------------------------------------------------------------
'
'----- Set variables before calling the waveform
capture subroutine -----
' (NOTE: There are no checks for correct data
form. All alpha characters
' MUST be capital letters. This should be no
problem since the
' input information is created in your program.)
'
ANA_IN$ =
"AB6" 'Analog input line used to input
waveform
SAMPLES = 1000 '# of
sample of data to store
TIME_DEL = 100 'Time
delay between each sample (msec)
TRIG$ = "AB6"
'Trigger source -(analog, digital, "" =
none)
TRIG_POL = 0 'Trigger
polarity (0=pos, 1=neg)
TRIG_V = 2.5 'DC trigger
voltage (volts) <optional>
'
'
'---- Place information in memory locations for
waveform capture routine to use ----
'
' Set the location for the beginning of data
storage
DATA_SEG=INT(PROG_SEG+(PROG_LEN/16)+1)
POKE
17EH,(DATA_SEG-(INT(DATA_SEG/256)*256))
'(LSB) Storage segment
POKE 17FH,DATA_SEG/256
'(MSB)
'
POKE
176H,(SAMPLES-(INT(SAMPLES/256)*256))
'(LSB) # of samples
POKE 177H,SAMPLES/256
'(MSB)
'
COUNT =
INT((TIME_DEL-42.2)/2.79611+0.5)+1
POKE
174H,(COUNT-(INT(COUNT/256)*256))
'(LSB) Delay between each sample
POKE 175H,COUNT/256
'(MSB)
'
ANA_MOD =
ASC(MID$(ANA_IN$,2,1))-41H
'ANALOG MODULE# (0-7)
DL=PEEK
((ANA_MOD-1)*2+14H)
'DL, DH = Module configuration data
DH=PEEK
((ANA_MOD-1)*2+15H)
RES = (DL AND 80H)/80H
'Analog Resolution (0=8-BIT, 1=12-BIT)
REF = (DL AND 40H)/40H
'Analog Reference (0=0V, 1=+/-V.)
F_SCALE = 5+((DH AND
8)/8*5)
'Full-scale analog voltage
'
POKE 17AH,(ANA_MOD*16)
OR (DL AND 0FH)
'Set Analog
in/out address
POKE
179H,(VAL(RIGHT$(ANA_IN$,(LEN ANA_IN$-2)))-(2*(DH
AND 7)))-1 'Analog line#
'
' ----- Set up the trigger information -----
TRIG=TRIG_V
IF REF=1 THEN
TRIG=TRIG+F_SCALE:F_SCALE=F_SCALE*2
X =
((256*((RES*15)+1))/F_SCALE)*TRIG
POKE 17BH,(X-(INT
(X/256)*256))
'(LSB) Trigger Voltage
POKE 17CH,X/256
'(MSB)
'
TRIG = 0
IF TRIG$=""
THEN GOTO L0
'No trigger
IF TRIG$=ANA_IN$ THEN
TRIG=TRIG OR 1:GOTO L0 'Analog
trigger
'
TRIG=TRIG OR
(ASC(MID$(TRIG$,2,1))-41H)16)
LINE_NUM =
VAL(RIGHT$(TRIG$,(LEN(TRIG$)-2)))
'Digital trigger line#
X = ((LINE_NUM-1)/8)-(DL
AND 0FH)
PORT = INT X
'Ttrigger port#
LINE = (X-INT X)*8
'line# in the digital port
POKE 17DH,(PORT*16 OR
LINE)
'Digital trigger port# & line#
'
L0: TRIG=TRIG+(TRIG_POL*80H)
'Trigger polarity
POKE 178H,(TRIG OR 2)
'Trigger source
'
'
'-------- Test for enough memory to store
waveform ----------
IF MEM_DATA <
(RES+1)*SAMPLES THEN BEEP:CLS:DISP
"INSUFFICIENT":DISP
"MEMORY!":END
'
SYS PROG_SEG,PROG_OFF
'Call the assembly subroutine
'
' At this point the waveform is in memory. If the
waveform is to be saved to the disk,
' use the following routine:
'
BEG_ADDR=DATA_SEG*16
'Address in RAM of the beginning of the data
S1 =
F_SCALE/((1+(RES*15))*256): S2 = REF*(F_SCALE/2)
'Voltage scaler multipliers
OPEN
"TRACE",OUT
'Open the disk file
FOR I=0 TO (SAMPLES-1)
STORE S1 *
(PEEK(I+BEG_ADDR)+PEEK(I+BEG_ADDR+1)*256) - S2
INC I : NEXT
CLOSE
'Close the disk file
'
/
NOTICE:
Every effort has been made to insure the accuracy
of the information contained in this document,
however
Y-tek is not responsible for any consequences
resulting from erroneous or inaccurate
information.
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