PXD10RM Datasheet, PDF (836/1332 Pages) Freescale Semiconductor, Inc – PXD10 Microcontroller

Tx/ Rx baud =
f_{periph_set_1_clk}
(16 × LFDIV)
Eqn. 23-1
LFDIV is an unsigned fixed point number. The 12-bit mantissa is coded in the LINIBRR and the fraction
is coded in the LINFBRR.
The following examples show how to derive LFDIV from LINIBRR and LINFBRR register values:
Example 23-1. Deriving LFDIV from LINIBRR and LINFBRR register values
If LINIBRR = 27d and LINFBRR = 12d, then
Mantissa (LFDIV) = 27d
Fraction (LFDIV) = 12/16 = 0.75d
Therefore LFDIV = 27.75d
Example 23-2. Programming LFDIV from LINIBRR and LINFBRR register values
To program LFDIV = 25.62d,
LINFBRR = 16 × 0.62 = 9.92, nearest real number 10d = 0xA
LINIBRR = mantissa (25.620d) = 25d = 0x19
NOTE
The baud counters are updated with the new value of the baud registers after
a write to LINIBRR. Hence the baud register value must not be changed
during a transaction. The LINFBRR (containing the Fraction bits) must be
programmed before the LINIBRR.
NOTE
LFDIV must be greater than or equal to 1.5d, i.e. LINIBRR = 1 and
LINFBRR = 8. Therefore, the maximum possible baudrate is
fperiph_set_1_clk / 24.
Table 23-1. Error calculation for programmed baud rates
= f_{periph_set_1_clk} MHz
= f_{periph_set_1_clk} 16 MHz
Baud
rate
Actual
Value programmed % Error =
in
(Calculated –
the baud rate
Desired)
register
baud rate
/ Desired
LINIBRR LINFBRR baud rate
Actual
Value programmed in
the baud rate register
LINIBRR LINFBRR
% Error =
(Calculated –
Desired)
baud rate
/ Desired
baud rate
10417 10416.7
384
0
–0.003
10416.7
96
0
–0.003
23-4
PXD10 Microcontroller Reference Manual, Rev. 1
Preliminary—Subject to Change Without Notice
Freescale Semiconductor