mcf51jf128 Freescale Semiconductor, Inc, mcf51jf128 Datasheet - Page 1111

• Manufacturer Part Number: mcf51jf128
• Description: Mcf51jf128 Reference Manual
• Manufacturer: Freescale Semiconductor, Inc

RT8, RT9, and RT10 samples are not all the same logical values. A framing error will
occur if the receiver clock is misaligned in such a way that the majority of the RT8, RT9,
and RT10 stop bit samples are a logic zero.
As the receiver samples an incoming frame, it re-synchronizes the RT clock on any valid
falling edge within the frame. Resynchronization within frames will correct a
misalignment between transmitter bit times and receiver bit times.
43.4.2.8.1 Slow data tolerance
The following figure shows how much a slow received frame can be misaligned without
causing a noise error or a framing error. The slow stop bit begins at RT8 instead of RT1
but arrives in time for the stop bit data samples at RT8, RT9, and RT10.
For an 8-bit data character, data sampling of the stop bit takes the receiver 154 RT cycles
(9 bit times × 16 RT cycles + 10 RT cycles).
With the misaligned character shown in the above figure, the receiver counts 154 RT
cycles at the point when the count of the transmitting device is 147 RT cycles (9 bit times
× 16 RT cycles + 3 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:
For a 9-bit data character, data sampling of the stop bit takes the receiver 170 RT cycles
(10 bit times × 16 RT cycles + 10 RT cycles).
With the misaligned character shown in the above figure, the receiver counts 170 RT
cycles at the point when the count of the transmitting device is 163 RT cycles (10 bit
times × 16 RT cycles + 3 RT cycles).
The maximum percent difference between the receiver count and the transmitter count of
a slow 9-bit character with no errors is:
Freescale Semiconductor, Inc.
((154 − 147) ÷ 154) × 100 = 4.54%
((170 − 163) ÷ 170) × 100 = 4.12%
RECEIVER
RT CLOCK
MCF51JF128 Reference Manual, Rev. 2, 03/2011
Figure 43-102. Slow data
MSB
Chapter 43 Universal Asynchronous Receiver/Transmitter (UART)
Preliminary
SAMPLES
DATA
STOP
1111