MC68HC11PH8 Datasheet, PDF (113/264 Pages) Motorola, Inc – High-density Complementary Metal Oxide Semiconductor (HCMOS) Microcomputer Unit

6.1.2 The pull field
The pull field consists of a pull synchronization bit, a pull data field and an end of frame. The pull
synchronization bit is a biphase coded ‘1’ and is initiated by the MCU during the time slot after the
last address bit of the push field. The pull data field consists of an NRZ coded transmission, each
bit taking one time slot. Once shifted in, the pull data is stored in the lower byte of the SCI data
register (S2DRL). The end-of-frame field is a square wave signal having a typical frequency of
20kHz ± 1% tolerance (i.e. the bit rate of the push field) when the data sent to the selected device
is valid.
6.2
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
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slot level. Bits are encoded as follows:
1 (set) – In the first time slot, the logic level is set to zero, followed by a logic
level one in the second time slot;
0 (clear) – In the first time slot, the logic level is set to one, followed by a logic
level zero in the second time slot.
Ô0Õ
Ô1Õ
Biphase coded signal
t
01234567 01234567
Biphase detection
Noise detection
a
aÕ a
b
bÕ b
a
aÕ a
b
bÕ b
Figure 6-2 Biphase coding and error detection
MC68HC11PH8
MOTOROLA INTERCONNECT BUS (MI BUS)
TPG
MOTOROLA
6-3