Siemens 500 NIM User Manual
Page 66
NIM Primitives
4-13
SIMATIC TIWAY I Series 500 NIM User Manual
Within the Descriptor Field (see Figure 4-3) are different fields to define the
following: data element types, location or address of a data element, number
of data elements to access, and the status of the attached device. The
Descriptor Field may contain a single descriptor or multiple descriptors as
required by the various Primitives.
Data Element Types — The length of the data element type descriptor field
is eight bits. This field, labelled “TT”, is a code that corresponds to the
different types of data found in the attached device. See Table 4-4 for a list
of data element types.
Current Status of Attached Device — Current status is designated by “HH”.
Number of Data Elements to access — This 16-bit field is designated by
“NNNN”. A value of one is interpreted as one location to be accessed. The
length of a location is determined by the data element type. The number of
locations requested should not exceed the maximum allowed for that device
type (see Table 4-4 and Table 4-5).
Data Element Location — Data element types are accessed by a location
number, designated by “AAAA” or “AAAA AAAA”. In the Series 500 NIM,
the location descriptor is a 16-bit value (32 bits if extended addressing is
used in the primitive code field). The allowable values for the location
number are shown in Table 4-5.
The format of the AAAA field changes for these TT types are:
(1)
TT Type 12 (Drum Count Preset) The format is:
AAAA = DD SS, AAAA AAAA = DDDD SSSS (extended
addressing)
where
DD = Drum Number
SS = Step Number (1 – 10
16)
(2)
TT types (36–3B, 76–7A) (Ramp Soak) The format is:
AAAA = LL SS or AAAA AAAA = LLLL LL SS (extended
addressing)
where
LL = Loop Number (1 – 40
16)
SS = Step Number (0 – FF
16)
The definition of the Basic Data Unit Field is dependent upon the data
element type specified in both the Descriptor Field and the Primitive format
definition. The Basic Data Unit is designated “DDDD” or “DD” in this
manual.
Descriptor Field
Basic Data Unit –
DDDD