MC68HC11PH8 Datasheet, PDF (114/264 Pages) Motorola, Inc – High-density Complementary Metal Oxide Semiconductor (HCMOS) Microcomputer Unit

6.3
Message validation
The communication between the MCU and the selected device is valid when the MCU reads a pull
data field having correct codes (excluding the codes ‘111’ and ‘000’) followed by a square wave
signal, having a frequency of 20kHz, contained in the end-of-frame information.
An MI BUS error is detected when the pull field contains the code ‘111’ followed by the
end-of-frame permanently tied to logical state ‘1’. This means that the communication between the
MCU and the selected device was not accomplished.
6.3.1 Controller detected errors
There are three different MI BUS error types which are detected by the selected slave device and
are not mutually exclusive. The MCU cannot determine which error occurred.
6
– Noise error Slave devices take two samples in each time slot of the biphase
encoded push field. An error occurs when the two samples for each time slot
are not the same logical level.
– Biphase error Slave devices receiving the push field detect the biphase
code. An error occurs when the two time slots of the biphase code do not
yield a logical exclusive-OR function.
– Field error A field error is detected when the fixed-form of the push field is
violated.
6.3.2 MCU detected errors
There is a fourth error that can be detected by the MCU. This error causes the noise flag (NF) to
be asserted in the S2SR1 register during the push field sequence.
– Bit error A bit error can be detected by the MCU during the push field. The
MI BUS serial system monitors the bus via on-chip hardware at the RXD pin
at the same time as sending data. A bit error is detected at that bit time when
the value monitored is different from the bit value sent.
MOTOROLA
6-4
MOTOROLA INTERCONNECT BUS (MI BUS)
TPG
MC68HC11PH8