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Chapter 33 Boot Assist Module (BAM)
MPC5602P Microcontroller Reference Manual, Rev. 4
836
Freescale Semiconductor
Higher baud rates high may be used, but the user will be required to ensure they fall within an acceptable
error range. This is illustrated in
, which shows the effect of quantization error on the baud
rate selection.
Figure 33-12. Baud rate deviation between host and MPC5602P
Example 33-4. Baud rate calculation for 250 kBaud signal
Considering reception of a 250kBaud signal from the host and MPC5602P operating with a 4 MHz
oscillator. Over 9 bits the time base will measure: (9 × 4e6)/250e3 = 144 cycles.
Thus, LINIBB is set to 144/144 = 1. This results in a baud rate of exactly 250 kBd.
However, a slower 225 kBd signal operating with 4 MHz XTAL would again result in LINIBB = 1, but
this time with an 11.1% deviation.
Table 33-11. Maximum and minimum recommended baud rates
f
sys
= f
xtal
(MHz)
Max baud rate for guaranteed
< 2.5% deviation
Min baud rate for guaranteed
< 2.5% deviation
4
13.4 Kbit/s
(SBR = 19)
30 bit/s
(SBR = 8192)
8
26.9 Kbit/s
(SBR = 19)
60 bit/s
(SBR = 8192)
12
38.4 Kbit/s
(SBR = 20)
90 bit/s
(SBR = 8192)
16
51.2 Kbit/s
(SBR = 20)
120 bit/s
(SBR = 8192)
20
64.0 Kbit/s
(SBR = 20)
150 bit/s
(SBR = 8192)
0
10000
Host baud rate
20000
30000
40000
50000
10.00
9.00
8.00
7.00
6.00
5.00
4.00
3.00
2.00
1.00
0.00
Baud rate deviation between host and device