UM10413
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© NXP B.V. 2011. All rights reserved.
User manual
Rev. 1 — 16 December 2011
99 of 268
NXP Semiconductors
UM10413
MPT612 User manual
The value of the U1FDR must not be modified while transmitting/receiving data or data
can be lost or corrupted.
If register U1FDR value does not comply to these two requests, then the fractional divider
output is undefined. If DIVADDVAL is zero, then the fractional divider is disabled, and the
clock is not divided.
15.3.4.1
Baud rate calculation
UART can operate with or without using the fractional divider. In real-life applications, it is
likely that the desired baud rate can be achieved using several different fractional divider
settings. The following algorithm illustrates one way of finding a set of DLM, DLL,
MULVAL, and DIVADDVAL values. Such set of parameters yields a baud rate with a
relative error of less than 1.1 % from that desired.
Fig 21. Algorithm for setting UART dividers
aaa-000584
DIVADDVAL = table(FR
est
)
MULVAL = table(FR
est
)
DLM = DL
est
[15:8]
DLL = DL
est
[7:0]
DIVADDVAL = 0
MULVAL = 1
true
End
PCLK,
BR
DL
est
is an
integer?
1.1 < FR
est
< 1.9?
DL
est
= PCLK/(16 × BR)
DL
est
= Int(PCLK/(16 × BR × FR
est
))
Pick another FR
est
from
the range [1.1, 1.9]
FR
est
= PCLK/(16 × BR × DL
est
)
FR
est
= 1.5
Calculating UART
Baud Rate (BR)
false
false
true