User's Manual

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RFI-148 & RFI-900 High Output Power Paging Transmitters User Manual Page 40 of 134
6.3.4 Page Datagram
The Page Datagram protocol is request-response. The maximum datagram length including the sync and CRC-
32 fields is 265 bytes. Any datagrams larger than this will be dropped without response.
The general format of the protocol is (size in bytes of field shown in parenthesis):
Sync (1)
0xCA
Length (2)
Type (1)
Source
Address (2)
Sequence
number (2)
Packet-specific-data (x)
CRC-32 (4)
Header
Footer
Figure 14: Page datagram generic format
The general fields are:
• Sync (1): The datagram sync byte, always 0xCA
• Length (2): The length of the datagram, minus the 3-byte header (sync, length) and 4-byte footer (CRC)
• Type (1): The type of the page datagram, see below
• Source Address (2): The address of the RTU to which the reply (if any) should be sent. This can be set
to 0xFFFF if unused
• Sequence number (2): An incrementing sequence number for confirming replies. This can be set to 0
if unused
• Packet-specific-data (x): Changes depending on the type field. Each type is shown in the following
section
• CRC-32 (4): 32-bit CRC generated by the polynomial 0xEDB88320, with a starting value of
0xFFFFFFFF and the resulting value XOR’d with 0xFFFFFFFF. The CRC-32 is generated over the
whole datagram excluding the Sync and CRC field.
PAGE SUBMIT
Submits a page message for transmission by the RFI PTX. The format of the page submit packet is shown in
Figure 15.
<header>
Message
length (2)
Baud rate
(2)
Message (x)
<footer>
Page
class (1)
Cap code
(4)
Function
override (1)
Figure 15: Page submission packet format
The fields are:
• <header>: The generic header shown in Figure 14 with the type field set to 0
• Message length (2): The length of the “Message (x)” field (the only variable length portion of this
packet)
• Baud rate (2): The baud rate as an integer (ie, 512, 1200, 2400).
• Page class (1): Determines the encoding of the message, one of: