Murata Electronics North America DNT900 Manual Do Utilizador
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©2008 by RF Monolithics, Inc.
E-mail: tech sup@rfm.com
DNT900 - 11/05/08
TDMA with PTT (Mode 4) supports remotes with a "push-to-talk" feature, also referred to as "listen-
mostly" remotes. This mode uses fixed slot allocations. Remotes can be registered for all but the last slot.
The last slot is reserved for the group of remotes that are usually listening, but occasionally need to
transmit. In essence, the last slot is a shared channel for this group of remotes. When one of them has
data to send it keys its transmitter much like a walkie-talkie, hence the name push-to-talk (PTT).
mostly" remotes. This mode uses fixed slot allocations. Remotes can be registered for all but the last slot.
The last slot is reserved for the group of remotes that are usually listening, but occasionally need to
transmit. In essence, the last slot is a shared channel for this group of remotes. When one of them has
data to send it keys its transmitter much like a walkie-talkie, hence the name push-to-talk (PTT).
The slot start time and the RemoteSlotSize are computed automatically by the DNT900 network in this
mode. The user must specify the number of slots. The last slot is reserved for the PTT remotes. The user
must configure PTT remotes individually to select Mode 4 operation. The network makes no guarantee
that PTT remote transmissions will not collide in the shared slot. The user's application must ensure that
no more than one PTT remote at a time is using the slot.
mode. The user must specify the number of slots. The last slot is reserved for the PTT remotes. The user
must configure PTT remotes individually to select Mode 4 operation. The network makes no guarantee
that PTT remote transmissions will not collide in the shared slot. The user's application must ensure that
no more than one PTT remote at a time is using the slot.
2.8 Network Configuration Planning
Some planning is necessary for a DNT900 network to coordinate the RF_DataRate, HopDuration, Bas-
eSlotSize
eSlotSize
, RemoteSlotSize, MinPacketLength, TxTimeout and TDMA_MaxNumSlots parameters to
achieve a practical configuration. This is true even for modes that automatically compute some of these
parameters. Each parameter has a limited range of usable values, as shown in the Table 2.8.1 below:
parameters. Each parameter has a limited range of usable values, as shown in the Table 2.8.1 below:
Parameter
Useable Range
Value
RF_DataRate
0..3
500, 200, 115.2 and 38.4 kb/s
HopDuration
40..4095
2. .204.75 ms (0.05 ms/count)
TDMA_MaxNumSlots
1 ..16
max number of TDMA slots (MNS) for remotes
BaseSlotSize
6..233
max number of user data bytes transmitted per hop
RemoteSlotSize
3..243
max number of user data bytes transmitted per hop
MinPacketLength
0..255
0. .255 bytes
Tx Timeout
0..255
0. .255 ms (1 ms/count)
Table 2.8.1
The highest RF data rate, 500 kb/s, provides the highest throughput and the most flexibility with respect
to the other parameters. The maximum RF power that can be used at 500 kb/s is 85 mW. The three lower
data rates can run up to 1 W of RF power, and the receiver becomes progressively more sensitive as the
data rate is lowered. So for greatest range, one of the three lower RF data rates should be used.
to the other parameters. The maximum RF power that can be used at 500 kb/s is 85 mW. The three lower
data rates can run up to 1 W of RF power, and the receiver becomes progressively more sensitive as the
data rate is lowered. So for greatest range, one of the three lower RF data rates should be used.
The maximum DNT900 HopDuration setting is about 200 ms regardless of the RF data rate chosen. For a
given data rate, FHSS operation tends to become more robust as hop duration is reduced. However,
running with a shorter hop duration may require setting the BaseSlotSize and RemoteSlotSize parame-
ters well below their maximum values at the lower RF data rates. The equation below calculates the
minimum hop duration needed at a given RF data rate for a specific number of remote slots and Base-
SlotSize
given data rate, FHSS operation tends to become more robust as hop duration is reduced. However,
running with a shorter hop duration may require setting the BaseSlotSize and RemoteSlotSize parame-
ters well below their maximum values at the lower RF data rates. The equation below calculates the
minimum hop duration needed at a given RF data rate for a specific number of remote slots and Base-
SlotSize
and RemoteSlotSize parameter settings. Support for optimizing a DNT900 configuration for a
specific application is also available from RFM’s Technical Support Group. See Section 10.3. for technical
support contact information.
support contact information.