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Use the RN (Delay Slots) parameter to configure this delay. Set RN = 0 (no delays) for small networks with few
repeaters or repeaters that are not within range of each other. Set RN = 1 for systems with two to five repeaters that
may be within range of each other.
The actual length of the delay is computed by the formula:
Delay (ms) = L * DS
DS = (-41-RSSI)/10*RN)+RandomInt(0,RN)
Where L is the length of the transmitted packet in milliseconds, DS is the number of delay slots to wait, RSSI is the
received signal strength in dBm, RN is the value of the RN register and RandomInt (A,B) is a function that returns a
random integer from A to B-0
Response packet delay
As a packet propagates through the repeater network, if any node receives the data and generates a quick response,
the network needs to delay the response so as not to collide with subsequent retransmissions of the original packet.
To reduce collisions, both repeater and end node devices in a repeater network delay transmission of data shifted in
the serial port to allow any repeaters within range to complete their retransmissions.
The time for this delay is computed by the formula:
Maximum Delay (ms) = L * DS
DS = ((-41-(-100))/10)*RN)+RN+1
Where L is the length of the transmitted packet in milliseconds, DS is the number of delay slots to wait, RSSI is the
received signal strength in dBm, and RN is the value of the RN register.
Use case - Broadcast Repeater network
Consider modules R1 through R10 each communicating to a PLC using the ModBus protocol and spaced evenly in a
line. All ten modules are configured as 'destinations and repeaters' within the scope of Basic Broadcast
Communications (MD=5, AM, DT=0xFFFF, PK=0x100, RO=0x03, RB=0x100, RN=1). The Base Host (BH) shifts payload
that is destined for R10 to R1. R1 initializes RF communication and transmits payload to nodes R2 through R5 which
are all within range of R1. The modules R2 through R5 receive the RF packet and retransmit the packet
simultaneously. They also send the data out the serial ports, to the PLCs. The following table shows commands used
to configure repeater functions.
AT
Command
AM
DT
MD
MY
RN
WR
XTend RF Module User Guide
Binary
AT Command
Command
Name
0x3A (58d)
Auto-set MY
0x00 (0d)
Destination Address
0x3C (60d)
RF Mode
0x2A (42d)
Source Address
0x19 (25d)
Delay Slots
0x08 (8d)
Write
Configure a repeater network
# Bytes
Range
Returned
-
-
0 - 0xFFFF
2
0 - 6
1
0 - 0xFFFF
2
0 - 0xFF [slots]
1
-
-
Factory
Default
-
0
0
0xFFFF
0
-
70
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