Analog Modules
5-7
S7-400, M7-400 Programmable Controllers Module Specifications
A5E00069467-07
5.3 Analog Value Representation
Introduction
This section describes the analog values for all the measuring ranges and output
ranges which you can use with the analog modules.

Converting Analog Values

Analog input modules convert the analog process signal into digital form.
Analog output modules convert the digital output value into an analog signal.

Analog Value Representation with 16-Bit Resolution

The digitized analog value is the same for both input and output values having the
same nominal range. The analog values are represented as a fixed-point number
in two’s complement. The resulting assignment is as follows:
Bit 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Value of bits 215 214 213 212 211 210 29282726252423222120

Bit 15 Can Be Interpreted as a Sign

The sign of the analog value is always contained in bit number 15:
”0” ³ )
”1” ³ *

Resolution Less than 16 Bits

If the resolution of an analog module has fewer than 16 bits, the analog value is
stored left-justified on the module. The lower-order bit positions not used are
padded with zeros (“0”).