PXR40RM Datasheet, PDF (953/1434 Pages) Freescale Semiconductor, Inc – PXR40 Microcontroller

Enhanced Serial Communication Interface (eSCI)
The baud rate generator is enabled when the TE bit or RE bit in the Control Register 1 (eSCI_CR1) is set
to 1 for the first time. The baud rate generator is disabled when SBR = 0.
Baud rate generation is subject to one source of error:
• Integer division of the module clock may not give the exact required target baud rate.
Figure 26-22 lists some examples of achieving target baud rates with a module clock frequency of
MCLK = 10.2 MHz.
Table 26-22. Baud Rates Error Example (MCLK = 10.2 MHz)
eSCI_BRR[SBR]
17
33
66
133
266
531
1062
2125
4250
5795
RCLK (Hz)
600,000.0
309,090.9
154,545.5
76,691.7
38,345.9
19,209.0
9604.5
4800.0
2400.0
1760.1
TCLK (Hz)
37,500.0
19,318.2
9659.1
4793.2
2396.6
1200.6
600.3
300.0
150.0
110.0
Target Baud Rate
38,400
19,200
9600
4800
2400
1200
600
300
150
110
Error (%)
2.3
.62
.62
.14
.14
.11
.05
.00
.00
.00
26.4.3.1 Module Clock
The module clock MCLK is derived from the system bus clock. It has the same phase and frequency.
26.4.3.2 Transmitter Clock
The transmitter clock TCLK is used to drive the data to the serial bus via the TXD pin. It is derived from
the system bus clock by the baud rate generator. The baud rate generator is controlled by the value of the
SBR field in the Baud Rate Register (eSCI_BRR). The frequency of the transmitter clock is determined
by Equation 26-1 and defines the length of the transmitted bits, which is denoted as the bit time.
f_TCLK
=
----^f--^M----^C----^L--^K-----
16  SBR
Eqn. 26-1
26.4.3.3 Receiver Clock
The receiver clock RCLK is used to sample the data received on the RXD or TXD pin. It is derived from
the system bus clock by the baud rate generator. The baud rate generator is controlled by the value of the
SBR field in the Baud Rate Register (eSCI_BRR). The frequency of the receiver sample clock is
determined by Equation 26-2.
f_RT
=
-^f--^M----^C---^L---^K-
SBR
Eqn. 26-2
Freescale Semiconductor
PXR40 Microcontroller Reference Manual, Rev. 1
26-25