User's Manual

Protocol Operation
Crescendo UHF Half-Duplex User Manual Page 41 of 78
 DP (2-bit): The destination serial port. This can be either 00 for the main port or 01 for the
auxiliary port.
 SP (2-bit): The source serial port. When sending a packet to a radio, this field does not need to be
set. The value will automatically be set to the serial port the packet was inserted on.
 Res (4-bit): Reserved for future use. This field should be set to all zeros.
 Data: The data to be transmitted. The amount of data in each datagram must be equal to or less
than the slot size.
 CRC (32-bit): A 32-bit CRC value calculated over the entire packet, excluding the Start and CRC
fields.
There are two options for the CRC field.
1. Fixed: The value is fixed to 0xEDB88320.
2. CRC: The CRC value is calculated using a 32-bit CRC with
 Initial Value: 0xFFFFFFFF
 Polynomial: 0xEDB88320
 Final XOR: 0xFFFFFFFF
When a radio modem receives a datagram packet over the air, the data will be output by the datagram
protocol in the same packet format as described in Figure 10.
An example Datagram packet with a calculated CRC-32 is shown in Figure 11.
Start
0xC1
Destination
0x0001
Source
0x0000
CRC
0x9496D61C
Data
0x54 0x45 0x53 0x54
DP / SP / Res
0x00
Length
0x0009
Figure 11: Example datagram protocol packet
Datagram protocol applications are given in section 7.4.
6.9 RF Link Status
The Crescendo provides an RF link status indication for each serial port. The RF link status depends on the
protocol mode being used and the current state of that protocol. The meaning of different RF link status
values is provided in Table 17 for each protocol mode.
Protocol
State
RF Link Status
Point-to-point
Connection Based
Connected if a path exists between the
local and remote device. Not Connected
if there is no communications path.
Connectionless
N/A
Point-to-multipoint
N/A
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