Enhanced Serial Communication Interface (eSCI)
MPC5565 Microcontroller Reference Manual, Rev. 1.0
20-20
Freescale Semiconductor
20.4.3
Baud Rate Generation
A 13-bit modulus counter in the baud rate generator derives the baud rate for both the receiver and the
transmitter. The value, 1 to 8191, written to the SBR0–SBR12 bits determines the system clock divider.
The SBR bits are in the eSCI control register 1 (ESCI
x
_CR1). The baud rate clock is synchronized with
the system clock and drives the receiver. The baud rate clock divided by 16 drives the transmitter. The
receiver has an acquisition rate of 16 samples per bit time.
Baud rate generation is subject to one source of error when integer division of the system clock does not
result in the exact target frequency.
lists some examples of achieving target baud rates with a system clock frequency of 128 MHz.
Table 20-15. Example of 8-bit Data Formats
Start
Bit
Data
Bits
Address
Bits
Parity
Bits
Stop
Bit
1
8
0
0
1
1
7
0
1
1
1
7
1
1
1
The address bit identifies the frame as an address char-
acter. Refer to
Section 20.4.5.6, “Receiver Wake-up
.”
0
1
Table 20-16. Example of 9-Bit Data Formats
Start
Bit
Data
Bits
Address
Bits
Parity
Bits
Stop
Bit
1
9
0
0
1
1
8
0
1
1
1
8
1
1
1
The address bit identifies the frame as an address char-
acter. Refer to
Section 20.4.5.6, “Receiver Wake-up
.”
0
1
Table 20-17. Baud Rates (Example: System Clock = 128 MHz)
Bits
SBR[0:12]
Receiver
Clock (Hz)
Transmitter
Clock (Hz)
Target Baud
Rate
Error
(%)
0x0023
3,657,143
228,571
230,400
–0.79
0x0045
1,855,072
115,942
115,200
+0.64
0x008B
920,863
57,554
57,600
–0.01
0x00D0
615,385
38,462
38,400
+0.16
0x01A1
306,954
19,185
19,200
–0.08
SCI baud rate
System clock
16
ESCIx_CR1[SBR]
×
-------------------------------------------------------------
=
Содержание MPC5565
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