22.5.5.1 Slow data toleranceFigure 22-4 shows how much a slow received frame can be misaligned without causing anoise error or a framing error. The slow stop bit begins at RT8 instead of RT1 but arrivesin time for the stop bit data samples at RT8, RT9, and RT10.MSBRT1RT2RT3RT4RT5RT6RT7RT8RT9RT10RT11RT12RT13RT14RT15RT16DATASAMPLESRECEIVERRT CLOCKSTOPFigure 22-4. Slow dataFor an 8-bit data and 1 stop bit character, data sampling of the stop bit takes the receiver9 bit times x 16 RT cycles +10 RT cycles =154 RT cycles.With the misaligned character shown in Figure 22-4, the receiver counts 154 RT cycles atthe point when the count of the transmitting device is 9 bit times x 16 RT cycles + 3 RTcycles = 147 RT cycles.The maximum percent difference between the receiver count and the transmitter count ofa slow 8-bit data and 1 stop bit character with no errors is:((154 - 147) / 154) x 100 = 4.54%For a 9-bit data or 2 stop bits character, data sampling of the stop bit takes the receiver 10bit times x 16 RT cycles + 10 RT cycles = 170 RT cycles.With the misaligned character shown in Figure 22-4, the receiver counts 170 RT cycles atthe point when the count of the transmitting device is 10 bit times x 16 RT cycles + 3 RTcycles = 163 RT cycles.The maximum percent difference between the receiver count and the transmitter count ofa slow 9-bit or 2 stop bits character with no errors is:((170 - 163) / 170) X 100 = 4.12%For a 9-bit data and 2 stop bit character, data sampling of the stop bit takes the receiver11 bit times x 16 RT cycles + 10 RT cycles = 186 RT cycles.With the misaligned character shown in Figure 22-4, the receiver counts 186 RT cycles atthe point when the count of the transmitting device is 11 bit times x 16 RT cycles + 3 RTcycles = 179 RT cycles.The maximum percent difference between the receiver count and the transmitter count ofa slow 9-bit and 2 stop bits character with no errors is: ((186 - 179) / 186) X 100 = 3.76%Chapter 22 Serial Communications Interface (SCI)MC9S08SU16 Reference Manual, Rev. 5, 4/2017NXP Semiconductors 417
