5.2.3. Data format of E20-10
Data format from
E20-10
in normal mode (by default) is 16-bit signed integers (in radix
complement) within the range of from -8192 to +8191. This means, that 14 low bits are information
ones and 2 high bits contain extended sign of radix complement. Binary the data looks like (15-th
bit is shown left, 0-th bit - right)
:
sssXXXXXXXXXXXXX
,
where,
s
– extended sign of radix complement,
X
– code positions
Lack of information content of two code high bits provides their value manipulation in
specific cases described in pp.
5.2.3.1.
Coding of word size overloading sign E20 -10 or
revision А
In
E20-10
of revision А the following coding of word size overloading sign is
applied (if the
relevant mode is activated): when no overloading, that data are transmitted unchanged, when
overloading – the data are transmitted with inverted 14-th data bit
š
:
s
š
sXXXXXXXXXXXXX
,
Based on radix complement representation of a number features, such inversion of 14-th bit,
in any way, will be cause of resulting value of 16-bit code over the range of -8192…+8191, – this
is software detectable sign of overloading.
In
E20-10
of revision В the word size overloading sign is not inserted in data format (p.
5.2.3.2.
Coding of data continuous area start in E20-10 of
revision B
In
E20-10
of revision В the data continuous area beginning ma
rker is applied which is coded
by inserting value "01" in field of positions <15..14>, if marker mode is activated:
01sXXXXXXXXXXXXX
,
Such representation of marker gives simple criteria of its software detecting - this is code
value over 8191.
14
In most programming languages, this format complies with "signed small integer".
