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SR/AI
SR/AP
Hardware Reference
Release r09
Page 18 of 76
3.5.2 Baud Rate Deviation
The information on how to set standard or custom baud rates can be found in [5]
Stollmann:
SR AT Command Reference.
Assumed that on both sides the TX and RX baud rates are nominally equal, the total baud rate
deviation is the sum of the host baud rate deviation and the SR baud rate deviation. The
total baud rate deviation shall not exceed 2.5% to prevent loss of data. Some margin should be
considered to cover deviations through the transmission line, e.g. due to asymmetry in low to high
and high to low transitions.
The following table shows the SR baud rate deviation in percent of the standard baud
rates caused by the baud rate generator granularity. Add 50ppm for the tolerance of the local
oscillator over the full temperature range.
Data Rate (bits/s)
Deviation (%)
9600
0.0
19200
0.0
38400
0.0
57600
0.0
115200
0.0
230400
0.0
460800
0.0
921600
0.0
Table 3: Standard Baud Rates and Deviations
Custom baud rates (CBR) are generated by a fractional divider according to the formula
𝐵𝑅
𝐻𝑧
=
14.745.600
16 [𝑀𝐴𝑁𝑇𝐼𝑆𝑆𝐴 +
𝐹𝑅𝐴𝐶𝑇𝐼𝑂𝑁
16
]
Where data types are for MANTISSA unsigned int12 and for FRACTION unsigned int4. These
values will be programmed to the fractional baud rate generator registers.
BR is the resulting baud rate which might not exactly be the targeted CBR due to the granularity
error of the fractional baud rate generator.
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