© Microhard Systems Inc.
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5.0 Network Topologies
5.2.4 Fast TDMA
A special version of TDMA, ‘Fast TDMA’ has been designed to minimize the TDMA cycle for
systems with large numbers of remote units, while maintaining the opportunity for each unit to
be able to transit its data. Fast TDMA is intended to sequence as many slaves as possible in
the shortest amount of time possible. It is based on the following diagram:
S
YN
C
Pa
cke
t
TDMA LIST
Con
tr
ol
D
at
a
(S
2
1
2
, S
1
1
2
)
2
20
11
5
1
7
5
S
YN
C
Pa
cke
t
FAST TDMA Frame
2
20
11
5
1
7
5
TDMA SLOTS (Intervals)
SL
2
SL
20
Ma
st
er
D
AT
A
D
AT
A
DATA
SYNC, TDMA List, Control Data, etc.
0
0
0
Figure 1: Fast TDMA Operation & Timing
At the start of a Fast TDMA Frame, the Master unit sends information to all the units in the TDMA net-
work. Included in this information is:
1)
SYNC Packet
- used for system synchronization.
2)
TDMA Table/List
- This is the list of all the addresses of all the remote units in the net-
work, as well as the order, and frequency in which they are to transmit data. Unit address-
es can be listed in any order, and can be listed multiple times to reduce latency. The Mas-
ter unit can be included in the table as unit address 1 if data is required to be transmitted
from the master to the remote units.
The TDMA Cycle/period depends on the size of the TDMA table. The current TDMA table
used for Fast TDMA operation is limited to 2048 entries. (128 entries are saved in non-
volatile memory and the rest of the entries must be re-entered every time on power up)
3)
Control Data
- Various control data such as the value of the Master units S212 register
(Max Expected Packet Size), and the Masters S112 register (Max Packet Size).
