Instrument Control Toolbox

The Record File Format

The record file is an ASCII file that contains a record of one or more instrument control sessions. You specify the amount of information saved to a record file with the RecordDetail property.

RecordDetail can be compact or verbose. A compact record file contains the number of values written to the instrument, the number of values read from the instrument, the data type of the values, and event information. A verbose record file contains the preceding information as well as the data transferred to and from the instrument.

Binary data with precision given by uchar, schar, (u)int8, (u)int16, or (u)int32 is recorded as hexadecimal values. For example, if the integer value 255 is read from the instrument as a 16-bit integer, the hexadecimal value 00FF is saved in the record file. Single- and double-precision floating-point numbers are recorded as decimal values using the %g format, and as hexadecimal values using the format specified by the IEEE Standard 754-1985 for Binary Floating-Point Arithmetic.

The IEEE floating-point format includes three components -- the sign bit, the exponent field, and the significand field. Single-precision floating-point values consist of 32 bits, and the value is given by

Double-precision floating-point values consist of 64 bits, and the value is given by

The floating-point format component, and the associated single-precision and double-precision bits are given below.

Format Component	Single-Precision Bits	Double-Precision Bits
sign	1	1
exp	2-9	2-12
significand	10-32	13-64

For example, suppose you record the decimal value 4.25 using the single-precision format. The record file stores 4.25 as the hex value 40880000, which is calculated from the IEEE single-precision floating-point format. To reconstruct the original value, convert the hex value to a decimal value using hex2dec:

• dval = hex2dec('40880000')
  dval =
      1.082654720000000e+009
  

Convert the decimal value to a binary value using dec2bin:

• bval = dec2bin(dval,32)
  bval =
  01000000100010000000000000000000
  

The interpretation of bval is given by the preceding table. The left most bit indicates the value is positive because (-1)⁰ = 1. The next 8 bits correspond to the exponent, which is given by

• exp = bval(2:9)
  exp =
  10000001
  

The decimal value of exp is 2⁷+2⁰ = 129. The remaining bits correspond to the significand, which is given by

• significand = bval(10:32)
  significand =
  00010000000000000000000
  

The decimal value of significand is 2^-4 = 0.0625. You reconstruct the original value by plugging the decimal values of exp and significand into the formula for IEEE singles:

• value = (-1)0(2129 - 127)(1.0625)
  value = 4.25
  

Specifying a Filename

Example: Recording Information to Disk