Configure a repeater network
9XTend-PKG-R RS-232/485 RF Modem User Guide
79
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 modems R1 through R10 each communicating to a PLC using the ModBus protocol and spaced evenly in a
line. All ten modems 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 modems 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
Binary
Command
AT Command
Name
Range
# Bytes
Returned
Factory
Default
AM
0x3A (58d)
Auto-set MY
-
-
-
DT
0x00 (0d)
Destination Address
0 - 0xFFFF
2
0
MD
0x3C (60d)
RF Mode
0 - 6
1
0
MY
0x2A (42d)
Source Address
0 - 0xFFFF
2
0xFFFF
RN
0x19 (25d)
Delay Slots
0 - 0xFF [slots] 1
0
WR
0x08 (8d)
Write
-
-
-