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Primitive Field Definitions (continued)
Primitive Field
Symbols
Length Field – LLLL
Primitive Code
Field – PP
Attached Device
Status – HH
4-12
NIM Primitives
The symbols used in the remainder of this section to denote the different
types of Primitive fields are summarized in Table 4-3.
Table 4-3 Summary of Primitive Field Symbols
Symbol
LLLL
PP
HH
TT
NNNN
AAAA or AAAA AAAA
DDDD
XX
CC
EEEE EEEE
YYYY
RRRR
MMMM
OOOO
The Length Field (refer to Figure 4-3) is a 16-bit field that represents the
length (in bytes) of the Primitive, Descriptor(s), and Data Unit field(s). The
Length Field is initialized by the Primary in transmissions to the NIM. It is
also initialized by the NIM in transmissions to the Primary. (Example: the
Length Field for a Primitive 02 request would have a value of 1.)
The Primitive Code Field (see Figure 4-3) is eight bits long, which allows for
256 unique Primitives. The most significant bit of the primitive field code is
used to designate that the extended addressing mode is in effect. In this
mode, the data element location descriptor is a 32-bit field rather than the
16-bit field associated with non-extended addressing.
The Series 500 NIM currently supports a subset of the Primitives: 00, 01,
02, 03, 04, 05, 06, 07, 10, 20, 21, 30, 31, 50, 51, 52, 55, 56, 57, 58, and 59.
The corresponding extended addressing codes are: 80, 81, 82, 83, 84, 85, 86,
87, 90, A0, A1, B0, B1, D0, D1, D2, D5, D6, D7, D8, and D9 (all values in
hexadecimal). These Primitive Codes are described in detail later in this
chapter.
The attached device status is updated by the NIM every four seconds. The
most recent attached device status is returned in most primitives.
Description
Length field
Primitive code
Attached device status
Data element types
Number of data elements
Data element location
Data unit(s)
Number of user-derfined structures requested
User-defined structure number
User-defined structure mask
Application sequence count
Host reference number
Attached device data segment definition
Attached device time-out value
SIMATIC TIWAY I Series 500 NIM User Manual
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