PXN20RM Datasheet, PDF (1016/1376 Pages) Freescale Semiconductor, Inc – PXN20 Microcontroller

Enhanced Serial Communication Interface (eSCI)
The maximum percent difference between the receiver baud rate and the transmitter baud rate is:
baudrate



r_---x_{---S---T---Or--x-P--S--}–_-T---Ot_--x_{-P---S--T---O---P-}

100
The maximum percent differences for the supported frames is given in Table 31-20
Eqn. 31-6
Table 31-20. Faster Receiver Maximum Tolerance
Payload Bits Max Baudrate Difference tx_STOP rx_STOP
8
4.63%
144 151
9
4.19%
160 167
13
3.03%
224 231
31.4.4.2 Slower Receiver Tolerance
In this case, the receiver has a slower baud rate than the transmitter, thus the stop bit sampling is still
running while the next start bit is already transmitted. To ensure the correct noise- and framing error-free
reception of the stop bit, the samples RS8, RS9, and RS10 must be located in the transmitted stop bit as
shown in Figure 31-24.
RXD
START BIT
LAST STOP BIT
START BIT
QUALIFICATION
DATA
VOTING
RCLK
RSC
678
12 3
Figure 31-24. Slower Receiver
8 9 10 11
The maximum tolerance that ensures error-free reception can be calculated with the assumption that RS11
is sampled in the transmitted start bit and RS10 is sampled in the last stop bit.
For an frame with n payload bits and s stop bits, the transmitter starts the transmission of the next start bit
tx_START = n + s + 1  16  RT_TR
after the start of the transmission of the previous start bit.
Eqn. 31-7
For an frame with n payload bits and s stop bits, the receiver samples the RS10 sample of the last stop bit
rx_STOP = n + s  16  RT_RE + 9  RT_RE
after the successful qualification of the start bit.
Eqn. 31-8
To ensure error-free reception of the last stop bit, the transmitter must start the transmission of the start bit
after the receiver samples RS10.
rx_STOP  tx_START
Eqn. 31-9
31-26
PXN20 Microcontroller Reference Manual, Rev. 1
Freescale Semiconductor