Digi M10 - Manual (Page 23)

Digi m10 Technical Overview
Digi International, Inc. © 2009 Page 23 of 26
4.6 RTS/CTS Control Packet
Table 7: RTS/CTS Control Packet
0 0x85/0x86
Packet Header
1 0x1D
Packet Type
2 Length0
Length of the packet
3 Length1
4 Retry_count/ Pkt Sequence Number
5 0/1
0 – Disable flow
control
1- Enable flow control
6 Fletch0
Fletcher Checksum
7 Fletch1
The checksum for the received LLACK, in response to DIGI m10 extended RTS/CTS
control packet sent by DTE, should be calculated for the first 5 bytes only.
Example:
On sending RTS/CTS enable/disable command, the LLACK that we receive is:
05 01 08 00 00 00 BD 35 and is 8 bytes in length.
However, in the above LL ACK response, the check sum should be calculated for the first 5 bytes
only for verification and byte marked in red should be ignored. That means we should calculate
checksum for “05 01 08 00 00” only, and validate it with the checksum embedded in the last two
bytes which is marked in green ( BD 35) in this example.
NOTE: DTE can enable or disable RTS/CTS flow control by sending the above packet.
DTE receives an 8 byte LLACK in response to the above packet.
Important:
1. Communication over USB will NOT work when RTS/CTS is enabled.
2. DTE should disable RTS/CTS flow control before connecting to the Digi m10
development board using USB.