MC68HC05E0 Datasheet, PDF (76/96 Pages) Motorola, Inc – High-density complementary metal oxide semiconductor (HCMOS) microcontroller unit

8.4
Transmission Error Detection
During a transmission sequence (i.e. only when sending data), the serial interface circuitry checks
for transmission errors caused by external influences (e.g. picture tube arcing). This transmission
error detection circuitry samples the state of the SDA output pin during transmission, using a
multiple of the transmission frequency, and compares the sampled value with an expected value
in an additional shadow register. The sampled values are filtered for every required value bit (i.e.
a majority decision is taken). The result of the comparison is shown in the Transmission Failure
Flag, TFF (bit 5 of the SI S Register, $0011) for each word transmitted. (See Figure 8-4.)
Serial Function
Data Register
Pad
Control
Shadow
Register
8
TFF
Comparator
Majority
Calculator
Sample
Logic
Sub-system Clock
Figure 8-4 Serial Interface Transmission Error Detection
MOTOROLA
8-10
SERIAL INTERFACE
MC68HC05E0