Instruction manual

Troubleshooting and Repair
025-9416 131
♦ Data block(s)
Each data block contains one page. A TNPP packet can contain more than
one data block if each page contains the same routing information (same
header). This field is limited in size only by the 1024 character maximum
per packet.
The Model 640 supports both full capcode paging and ID paging for
TNPP networking. Each type of data block has a slightly different format.
See Table 25 and Figure 67 for details on the data block fields.
♦ End Flag
ETX “♥.” This field is 1 character long and remains constant.
♦ CRC-16 BCC
(block check code)
The CRC-16 is a 2-character error-detection protocol. Usually the CRC
information consists of strange looking control characters.
Communication errors are very unlikely to go undetected when using
CRC-16.
Here is how a typical capcode page packet might look on a PC:
JDE000801015C AGNA@C0040067298888005
♥
=K
CRC
Header
Page Block
Because the delimiters in the packet are control characters, some terminal emulators might show
the funny characters like:
^ADE000801015C^BAGNA@C0040067298888005^C=K
Header Elements
The packet header is 12 characters in length and includes four pieces of information. The header
structure is shown in Figure 65.
Destination address
(4)
Source address
(4)
Inertia
(2)
Serial number
(2)
Figure 65. Header Structure
Table 24 describes each header element and the possible values. Note that the “Example” column
identifies the element in the example packet above.
Table 24. TNPP Packet Header Fields
Example Valid Entries Description
DE00 4 hex digits
0001 - FFFF
Destination address - the node the packet designated for
08 2 hex digits
00 - FF
Inertia - controls the maximum number of “hops” in a network
0101 4 hex digits
0001 - FFFF
Source address - the originating node