© Microhard Systems Inc. Confidential 88
In PP/PMP S115 determines the number of slots which are available within a window of opportunity for Remote units
to submit channel requests to the Master modem. For a large number of remotes, the value of S115 should be set
relatively high: Remotes will randomly contend for the ability to access the channel request slots. For a small
number of Remotes, it is advisable to keep S115 closer to the default value so as to not ‘waste bandwidth’ by
maintaining a relatively large window housing a greater-than-necessary number of channel reservation request slots.
6.0 Register/Command Reference
Values (0 - 254)
5
S113 Packet Retransmissions
This register determines the maximum number of times that a packet will be
retransmitted (in addition to the initial transmission). Retransmissions can be
used to provide system robustness and to ensure data delivery due to noisy
environments or weak signal levels. Retransmissions should not be used as the
only means to correct for data collisions. Retransmissions create additional
traffic and can have a significant impact on overall throughput of a system.
Values (1 - 256)
S112 Packet Max Size
256
Determines that maximum number of bytes from the connected device that will
be encapsulated into a packet unless the character timeout timer S116 expires.
Large packet sizes may produce the best data throughput; however, a smaller
packet is less likely to become corrupted and, if it does, is retransmitted with a
lesser impact on network traffic. The default setting of 256 bytes is suited to
most applications.
Values (0 - 255)
5 (Mesh), 3 (PP/PMP)
S115 Repeat Interval
In Mesh S115 defines the randomness of accessing the channel (0 - 255). The
bigger the number, the less often attempts are made to access the channel,
resulting in lower collisions, but at the cost of added latency.
Values (1 - 255)
S111 Packet Min Size
1
This is the minimum number of collected bytes in one buffer before the buffer
can be closed by the character timeout timer controlled by S116. It is
STRONGLY advised not to modify this parameter. Changing S111 may prevent
the modem from detecting the escape sequence.
In a PMP system, set
S113 to the minimum
value required as,
effectively, the data
throughput from Master to
Remote is divided by 1
plus the number stored in
S113.
Values (10 - 254)
10
S116 Character Timeout
Character Timeout in 1/4 of character time (10-255). Default = 10 (2.5
character time). This ‘timer’ looks for gaps in the data being received from the
local attached device. The timer is activated after the Minimum Packet Size
(S111, default 1 Byte) has been accumulated in the modem. If the timer detects
a gap in the data exceeding the Character Timeout value, the modem will
transmit the data.
The Pico will accumulate data in its buffers until either (a) Maximum Packet size (S112) has been accumulated, or
(b) Minimum Packet Size (S111) has been accumulated AND the Character timeout has expired—whichever occurs
first.
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