Siemens 500 NIM User Manual
Page 58
NIM Primitives
4-5
SIMATIC TIWAY I Series 500 NIM User Manual
Figure 4-1 illustrates the basic Primitive structure when HDLC operation is
selected. There is a Request Format and a Response Format, as shown. The
binary weight of the fields is detailed in Figure 4-2. All field lengths are
multiples of 8 bits, which allows for octet testing of data link frames at the
data link/media access control layer.
HDLC I Frame or UI Frame
Flag Address Control Information
FCS
Flag
Bit
0
8
16
24
N - 24
N - 8
N
Length
Primitive Code Descriptor(s) Data Unit(s)
Primitive Fields
Request Format
Response Format
MSB
LSB
Length Prim / Error Secondary Status Data Unit(s)
Figure 4-1
Basic Primitive Structure
The maximum length of the Information field is 273 bytes for the Series 500
NIM. In the Request format, the 273 bytes include the Length, Primitive
code, Descriptor, and Data Unit fields. In the Response format, the 273
bytes include the Length, Primitive Code/Error, Secondary Status, and Data
Unit fields. In both formats, the 273 bytes exclude the protocol control
fields. Other devices connected to TIWAY I may support Information Field
lengths in excess of 273 bytes. The actual length support is dependent on
device type and must be ascertained with the Format Configuration
Primitive 04.