SRS Labs SR850 manual Trcl ? i, j, k

Remote Programming

	transfer does not pause between bytes. The receiving interface must
	always be ready to receive the next byte. In general, using binary trans-
	fers on the RS232 interface is not recommended.
	The parameter i selects a trace (1, 2, 3 or 4) and is required. If Trace i is
	not stored, then an error occurs. Points are read from the buffer starting
	at bin j (j≥0). A total of k bins are read (k≥1) for a total transfer of k*4
	bytes. To read a single point, set k=1. Both j and k are required. If j+k
	exceeds the number of stored points (as returned by the SPTS? query),
	then an error occurs. Remember, SPTS? returns N where N is the total
	number of bins - the TRCB? command numbers the bins from 0 (oldest)
	to N-1 (most recent).
TRCL ? i, j, k	The TRCL? command queries the points stored in Trace i. The values
	are returned in a non-normalized floating point format (with the units of
	the trace). There are 4 bytes per point. Multiple points are not separated
	by any delimiter. The bytes CANNOT be read directly into a floating point
	array.
	Each point consists of four bytes. Byte 0 is the LSB and Byte 3 is the
	MSB. The format is illustrated below.
		16 bits		16 bits
		0	exp	mantissa
		byte3	byte2	byte1	byte0

The mantissa is a signed 16 bit integer (-32768 to 32767). The exponent is a signed integer whose value ranges from 0 to 248 (thus byte 3 is always zero). The value of a data point is simply,

value = m x 2 (exp-124)

where m is the mantissa and exp is the exponent.

The trace data within the SR850 is stored in this format. Data transfers using this format are faster than IEEE floating point format. If data trans- fer speed is important, the TRCL? command should be used.

Do not query the IFC (no command in progress) status bit after sending the TRCL command. This bit will not be set until the transfer is complete.

When using the GPIB interface, EOI is sent with the final byte. The points must be read using a binary transfer (see your GPIB interface card soft- ware manual). Make sure that the software is configured to NOT termi- nate reading upon receipt of a CR or LF.

When using the RS232 interface, the word length must be 8 bits. The points must be read as binary bytes (no checking for linefeeds, carriage returns or other control characters). Most serial interface drivers are designed for ASCII text only and will not work here. In addition, the data transfer does not pause between bytes. The receiving interface must always be ready to receive the next byte. In general, using binary trans- fers on the RS232 interface is not recommended.

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