Managing the Radio | 157
Aprisa SR+ User Manual 1.11.1
Serial data port variable parameters
Two key serial port parameters will be adjusted during optimization. The following initial values have been
determined as a suitable for the SEL 2505 device which is the fastest device 4RF has lab tested. It is a
suitable start point to carry out optimization for other devices.
Inter-Frame Gap
–
initially set to 0.2
•
IFG is dependent on serial line baud rate only
•
The Mirrored Bits® protocol is essentially timed to a base clock, the slower the baud rate the longer
the period to transmit a packet resulting in less time between packets
•
A low baud rate is ideal as it increase the time period before a ROK error will occur as this is
dependent on serial packet transmission time
•
The minimum baud rate currently proven to provide reliable communications is 9600 bit, with this
rate an IFG of 0.2 is required to be used
•
With the 2505 device the IFG increases with increases in serial baud rate, while easier to detect
gaps the ROK error period is reduced
MTU
–
initially set to 32 bytes
•
Dependent on serial line baud rate, channel size, modulation, security settings, intended traffic mix
and all other settings that influence OTA speed and capacity available for external traffic
•
MTU affects latency, if a large
MTU then the radio will ‘wait’
for the number of bytes before sending
the packet OTA
•
Ideally a low MTU will be used
–
the minimum needs to support the various settings above and
intended mix of traffic
•
MTU can be changed in steps of +/- 8 when trying different configurations
•
Refer table in section 5 for start point of MTU based on channel size, modulation and serial baud
rate, this assumes the general radio settings as above
•
Increase by 8 for new devices or in attempt to support some Ethernet or other services
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