MC68HC08AS32A Datasheet, PDF (183/296 Pages) Motorola, Inc – Microcontrollers

Freescale Semiconductor, Inc.
Serial Communications Interface (SCI)
Functional Description
MSB
STOP
RECEIVER
RT CLOCK
DATA
SAMPLES
Figure 13-8. Slow Data
The maximum percent difference between the receiver count and the transmitter
count of a slow 8-bit character with no errors is
-1---5---4-----^–----1----4---7-- ^{× 100 = 4.54%}
154
For a 9-bit character, data sampling of the stop bit takes the receiver
10 bit times × 16 RT cycles + 10 RT cycles = 170 RT cycles.
With the misaligned character shown in Figure 13-8, the receiver counts 170 RT
cycles at the point when the count of the transmitting device is
10 bit times × 16 RT cycles + 3 RT cycles = 163 RT cycles.
The maximum percent difference between the receiver count and the transmitter
count of a slow 9-bit character with no errors is
-1---7---0-----^–----1----6---3-- ^{× 100 = 4.12%}
170
Fast Data Tolerance
Figure 13-9 shows how much a fast received character can be misaligned without
causing a noise error or a framing error. The fast stop bit ends at RT10 instead of
RT16 but is still there for the stop bit data samples at RT8, RT9, and RT10.
STOP
IDLE OR NEXT CHARACTER
RECEIVER
RT CLOCK
DATA
SAMPLES
Figure 13-9. Fast Data
For an 8-bit character, data sampling of the stop bit takes the receiver
9 bit times × 16 RT cycles + 10 RT cycles = 154 RT cycles.
MC68HC08AS32A — Rev. 1
MOTOROLA
Serial Communications Interface (SCI)
For More Information On This Product,
Go to: www.freescale.com
Data Sheet
183