Freescale Semiconductor, Inc.
Motorola Interconnect Bus (MI BUS)
Biphase coding
6.6 Biphase coding
Manchester biphase L coding is used for the push field bits. Each bit
requires two time slots to encode the logic value of the bit. This encoding
allows the detection of a single error at the time slot level. Bits are
encoded as follows:
1 = In the first time slot, the logic level is set to zero, followed by a
logic level one in the second time slot;
0 = In the first time slot, the logic level is set to one, followed by a
logic level zero in the second time slot.
‘0’
‘1’
Biphase coded signal
t
0
1
2
3
4
5
6
7
0
1
2
3
4
5
6
7
a
a
b
b
a
a
b
b
Biphase detection
Noise detection
a’
b’
a’
b’
Figure 6-2. Biphase coding and error detection
6.7 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.
MC68HC11P2 — Rev 1.0
Technical Data
Motorola Interconnect Bus (MI BUS)
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