User's Manual

9XTend™ OEM RF Module - Product Manual v2.x6x
© 2010 Digi Internatonal, Inc. 54
Polling Mode (Acknowledged)
NOTE: Polling Mode (Acknowledged) and Polling Mode (Basic) [p50] operate in the same way. The
difference between the two modes is in their means of achieving reliable delivery of data. In Poll-
ing Mode (Acknowledged), reliable delivery is achieved using retries and acknowledgements.
Attributes:Utilizes high percentage of available network bandwidth
Eliminates collisions
Works with reliable delivery (RR or MT parameters)
Supports binary data transfers
Base module requests packets from remote module by polling a sequential 
range of addresses
Base module is con
figured to specify the range of addresses being polled
Uses inter-character delay to create RF packet lengths aligned with protocol 
packet lengths up to 2048 bytes long.
Required Parameter Values (Base): MD (RF Mode) = 3, PB (Polling Begin Address), PE (Polling
End Address)
Required Parameter Values (Remote): MD (RF Mode) = 4
Related Commands: Networking (RR, PD, DT, MY, AM)
Constraints: The minimum time interval between polling cycles is configurable. However, if the
remote modules cannot all be processed within tha
t time interval, the polling cycle is ineffective
(i.e. it will impose no additional delay). In order to ensure a pause between polling cycles, PD
must be set to a value which is large enough to accommodate the pause.
Recommended Use: Use for point-to-multipoint applications that require Reliable Delivery of
data. Use this mode when it is critical that a base module be able to discern data coming from
multiple modules.
Theory of Operation
A ‘Polling Base’ module will cycle through a sequential range of addresses. The ‘Polling Base’ will
poll each ‘Polling Remote’ module, wait for a response, then poll the next remote address in the
sequence. Each ‘Polling Remote’ will respond by sending the data from its DI (Data In) buffer fol-
lowing the RB (Packetization Threshold) & RO (Packetization Timeout) parameters. When there is
no eligible data to send, the ‘Polling Remote’ will not respond. The ‘Polling Base’ will poll the next
address in the polling sequence after a short delay.
Polling Base
Configuration:
Polling Remote Configuration:
Set the MD (RF Mode) parameter (MD = 3).
Set MY (Source Address) parameter (MY = 0).
Set the sequential range of Polling Addresses using the PB (Polling Begin Address) and PE
(Polling End Address) parameters.
(Optional) Enable Acknowledged Reliable Delivery (RR >= 0). Note: Basic Reliable Delivery is
also supported. Refer to the ‘Polling Mode - Basic section for more information.
(Optional) Use the PD (Minimum Polling Delay) command to configure a delay between polls to
slow down system (if needed).
(Optiona
l) Enable API Mode to address remotes within polling range on a packet-by-packet
basis.
Set the MD (RF Mode) parameter (MD = 4).
Configure sequential source addresses for all remote modules using the MY (Source Address)
command.
Set the DT (Destination Address) parameter to point to ‘Polling Base’ (DT = 0x0000).
(Optional) Enable Acknowledged Reliable Delivery (RR >= 0). Note: Basic Reliable Delivery is
also supported. Refer to the ‘Polling Mode - Basic section for more information.