MC68HC05E5 Datasheet, PDF (72/140 Pages) Freescale Semiconductor, Inc – General Release Specification

Freescale Semiconductor, Inc.
Motorola Bus (M Bus) Interface
11.5.1 Start Signal
When the bus is free (for example, no master device is engaging the bus
and both SCL and SDA lines are at logical high), a master may initiate
communication by sending a start signal. As shown in Figure 11-1, a
start signal is defined as a high-to-low transition of SDA while SCL is
high. This signal denotes the beginning of new data transfer (each data
transfer may contain several bytes of data) and wakes up all slaves.
MSB
LSB
SCL
11000011
ACKNOWLEDGE BIT
SDA
START SIGNAL
MSB
LSB
11000011
NO ACKNOWLEDGE
STOP SIGNAL
MSB
LSB
MSB
LSB
SCL
11000011
11000011
ACKNOWLEDGE BIT
NO ACKNOWLEDGE
SDA
START SIGNAL
REPEATED START SIGNAL
Figure 11-1. M-Bus Transmission Signal Diagram
STOP SIGNAL
General Release Specification
Motorola Bus (M Bus) Interface
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MC68HC05E5 — Rev. 1.0