Fluke PM-3370B, PM-3380B, PM-3390B, PM-3394B, PM-3384B user manual Byte1 = ASCMID$response$, J

USING THE COMBISCOPE INSTRUMENTS 3 - 33

3.4.3.2Conversion of 16-bit samples to integer

As an example a conversion of a trace of 512 "16-bit" samples is shown. The format is as follows:

trace bytes

# 4 1 0 2 6 <16> <msb 1> <lsb 1> . . . <msb 512> <lsb 512> <checksum> <NL>

trace sample 512 trace sample 1

byte with decimal value 16 number of trace bytes (1026) number of digits of 1026

PROGRAM EXAMPLE:

In this example a trace acquisition of 2 byte samples is done. Thereafter, the trace data is read and converted to integer samples in the array "trace", and the number of trace bytes samples is printed. The conversion from double byte (byte1 = msb and byte2 = lsb) to integer is done as follows (refer to figure 3.12):

If byte1 < 128 then integer = byte1 * 256 + byte2.

If byte1 ≥ 128 then integer = (byte1 - 256) * 256 + byte2.

Example: byte1 = 255 & byte2 = 32 --> integer = (255 - 256) * 256 + 32 = - 224.

DIM trace(512)		’Array of 512 integers
DIM response AS	STRING * 1033	’Trace response buffer
CALL Send(0, 8,	"*RST", 1)	’Resets the instrument
		’Sets 16 bit sample data format
CALL Send(0, 8,	"INITiate", 1)	’Single shot initiation
CALL Send(0, 8,	"*WAI;TRACe? CH1", 1)	’Queries for channel 1 trace
CALL Receive(0,	8, response$, 256)	’Reads the channel 1 trace
PRINT "Number of trace bytes ="; IBCNT%		’IBCNT% = length of trace buffer
’

’The contents of the response$ string of this example will be as follows: ’# 4 1 0 2 6 <16> <msb1> <lsb1> ... <msb512> <lsb512> <sum> <10>

’

nr.of.digits = VAL(MID$(response$, 2, 1))

nr.of.bytes = VAL(MID$(response$, 3, nr.of.digits)) - 2 PRINT "Number of trace bytes ="; nr.of.bytes sample.length = ASC(MID$(response$, 3 + nr.of.digits, 1)) nr.of.samples = nr.of.bytes / (sample.length / 8)

PRINT "Number of trace samples ="; nr.of.samples FOR i = 1 TO nr.of.samples

J = 2	* i + 2 +	nr.of.digits	’Pointer to next sample
byte1	= ASC(MID$(response$, J, 1))		’Most Significant Byte
byte2	= ASC(MID$(response$, J + 1, 1))		’Least Significant Byte

IF byte1 < 128 THEN

trace(i) = byte1 * 256 + byte2

ELSE trace(i) = (byte1 - 256) * 256 + byte2

END IF NEXT i