X09-009NSC-TX Digi International/Maxstream, X09-009NSC-TX Datasheet - Page 40

• Manufacturer Part Number: X09-009NSC-TX
• Description: MOD RF TX 900MHZ 9600BPS W/RPSMA
• Manufacturer: Digi International/Maxstream

Specifications of X09-009NSC-TX

• Frequency: 900MHz
• Data Rate - Maximum: 19.2kbps
• Modulation Or Protocol: FSK
• Power - Output: 100mW
• Sensitivity: -110dBm
• Voltage - Supply: 5V
• Current - Receiving: 50mA
• Current - Transmitting: 140mA
• Data Interface: PCB, Through Hole
• Antenna Connector: RP-SMA
• Operating Temperature: 0°C ~ 70°C
• Package / Case: Module
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Applications: -
• Memory Size: -

XStream™ OEM RF Module – Product Manual v5.x00 [2006.02.24]
Use Case - Broadcast Repeater Network
Response packet delay
As a packet propagates through the repeater network, if any node receives the data and
generates a quick response, the response needs to be delayed so as not to collide with
subsequent retransmissions of the original packet. To reduce collisions, both repeater and end
node radios in a repeater network will 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:
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.
Consider modules R1 through R10 each communicating to a PLC using the ModBus protocol and
spaced evenly in a line. All ten nodes are configured as ‘destinations & repeaters’ within the
scope of Basic Broadcast Communications (MD=3, 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. Modules R2 through R5 receive the RF packet and retransmit the packet
simultaneously. They also send the data out the serial ports, to the PLC's.
Table 4‐03. Commands used to configure repeater functions
AT
Command
AM
DT
MD
MY
RN
WR
Bandwidth Considerations
Using broadcast repeaters in a network reduces the overall network data throughput as each
repeater must buffer an entire packet before retransmitting it. For example: if the destination is
within range of the transmitter and the packet is 32 bytes long, the transmission will take 72ms
on a 9600 baud XStream Module (much faster modules are available). If that same packet has to
propagate through two repeaters, it will take 72ms to arrive at the first repeater, another 72 ms
to get to the second and a final 72ms to get to the destination for a total of 216ms. Taking into
account UART transfer times (~1ms/byte at 9600 baud), a server to send a 32 byte query and
receive a 32 byte response is ~200ms, allowing for 5 polls per second. With the two repeaters in
the path, the same query/response sequence would take about 500ms for 2 polls per second.
To summarize, this system is sending and receiving 64 bytes 5 times per second for a throughput
of 320 bytes per second with no repeaters and 128 bytes per second with 2 repeaters. Generally,
the network throughput will decrease by a factor of 1/(R+1), with R representing the number of
repeaters between the source and destination.
Note that these numbers are absolutely worst case to illustrate how the system would perform in
a typical, low bandwidth system. As a counter example the 115kbps 9XTend radio can transfer
the same 32 byte packet in 12 ms for a round trip with UART transfer times of ~30ms or 33 polls
per second (1066 bytes per second) with no repeaters. With two repeaters the time would be
~100ms round trip time for 10 polls per second or 320 bytes per second network throughput with
two repeaters.
© 2006 MaxStream, Inc. Confidential and Proprietary
Maximum Delay (ms) = L * DS
DS = ((-41-(-100))/10)*RN)+RN+1
Binary
Command
0x3A (58d)
0x00 (0d)
0x3C (60d)
0x2A (42d)
0x19 (25d)
0x08 (8d)
AT Command Name
Auto-set MY
Destination Address
RF Mode
Delay Slots
Write
Source Address
Range
-
0 – 0xFFFF
3 - 4
0 – 0xFFFF
0 – 0xFF [slots]
-
-
-
# Bytes
Returned
2
1
2
1
Factory
Default
-
0
0
0xFFFF
0
-
40