MPC5553/MPC5554 Microcontroller Reference Manual, Rev. 5
Freescale Semiconductor
21-29
For an 8-bit data character, data sampling of the stop bit takes the receiver RT clock 151 clock cycles, as
is shown below:
With the misaligned character shown in
, the receiver counts 151 RT cycles at the point when
the count of the transmitting device is 9 bit times x 16 RT cycles = 147 RT cycles.
The maximum percent difference between the receiver count and the transmitter count of a slow 8-bit data
character with no errors is 4.63%, as is shown below:
For a 9-bit data character, data sampling of the stop bit takes the receiver 167 RT cycles, as is shown below:
With the misaligned character shown in
, the receiver counts 167 RT cycles at the point when
the count of the transmitting device is 10 bit times x 16 RT cycles = 160 RT cycles.
The maximum percent difference between the receiver count and the transmitter count of a slow 9-bit
character with no errors is 4.19%, as is shown below:
21.4.5.5.2
Fast Data Tolerance
shows how much a fast received frame can be misaligned. The fast stop bit ends at RT10
instead of RT16 but is still sampled at RT8, RT9, and RT10.
Figure 21-20. Fast Data
For an 8-bit data character, data sampling of the stop bit takes the receiver 154 RT cycles, as is shown
below:
With the misaligned character shown in
, the receiver counts 154 RT cycles at the point when
the count of the transmitting device is 10 bit times x 16 RT cycles = 160 RT cycles.
The maximum percent difference between the receiver count and the transmitter count of a fast 8-bit
character with no errors is 3.40%, as is shown below:
9 bit times
16 RT cycles
7 RT cycles
+
151 RT cycles
=
151 – 144
151
--------------------------
100
4.63%
=
10 bit times
16 RT cycles
7 RT cycles
+
167 RT cycles
=
167 – 160
167
--------------------------
100
4.19%
=
RT1
Receiver
RT Clock
RT2
RT3
RT4
RT5
RT6
RT7
RT8
RT9 RT10 RT11 RT12 RT13 RT14 RT15 RT16
STOP
IDLE or Next Frame
Data Samples
9 bit times
16 RT cycles
10 RT cycles
+
154 RT cycles
=
160 – 154
160
--------------------------
100
3.40%
=
Summary of Contents for MPC5553
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