Freescale Semiconductor, Inc.
Motorola Interconnect Bus
16.5.1 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.
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.
16.5.2 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 SC0SR1 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 RxD0 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.
16.6 Interfacing to MI Bus
Physically the MI Bus consists of only a single wire. In the example
shown in Figure 16-4, only a single transistor and a few passive
components are required to connect up the 68HC(9)12D60 for full
MI Bus operation.
Advance Information
268
68HC(9)12D60 — Rev 4.0
Motorola Interconnect Bus
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