NIM Primitives
4-10
TIWAY 1 TI505 NIM User Manual
4.5.3
Primitive Code Field – PP
The Primitive Code Field is eight bits long, which allows for 256 unique Primitives. The
most significant bit of the Primitive field code designates whether extended addressing
is in effect. If extended addressing is used, the data element location descriptor is a 32-bit
field rather than the 16-bit field associated with non-extended addressing.
The Series 505 NIM currently supports a subset of the Primitives: 00, 01, 02, 03,
04, 05, 10, 20, 21, 30, 31, 50, 51, 52, 55, 56, and 57. The correspondingextended
addressingcodes are: 80, 81, 82, 83, 84, 85, 90, A0, A1, B0, B1, D0, D1, D2, D5,
D6, and D7 (all values in hexadecimal). Detailed Primitive descriptions are proĆ
vided later in this chapter.
4.5.4
Descriptor Field
Within the Descriptor Field 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 Type — The length of the data element type descriptor field is eight bits.
This field, labeled “TT”, is a code that corresponds to the different types of data found in
the attached device. See Table 4Table 4 for a list of data element types.
Attached Device / NIM Status — The eight bit “HH” field designates the current status.
The attached device status is updated by the NIM every four seconds. The most recent
attached device status is returned in most Primitives. See the Status Primitive descrip-
tion for additional information.
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 maxi-
mum allowed for that device type (see Tables 4Table 4 and 4Table 5). If you are using
packed discrete format, the data will be returned in groups of 8 bits. For example, if you
request 10 data elements, 2 bytes will be returned.
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