
MOTOROLA
MC68307 USER’S MANUAL
7-1
SECTION 7
M-BUS INTERFACE MODULE
Motorola bus (in short: M-bus) is a two-wire, bidirectional serial bus which provides a simple,
efficient method of data exchange between devices. It is compatible with the widely-used
I2C bus standard. This two wire bus minimizes the interconnection between devices and
eliminates the need for an address decoder.
This bus is suitable for applications which need occasional communications in a short dis-
tance among a number of devices. It also provides flexibility that allows additional devices
to be connected to the bus for further expansion and system developing.
The interface is designed to operate up to 100 Kb/s with maximum bus loading and timing.
The device is capable of operating at higher baud rates, with reduced bus loading. The max-
imum communication length and number of devices that can be connected are limited by a
maximum bus capacitance of 400 pF.
M-bus system is a true multi-master bus including collision detection and arbitration to pre-
vent data corruption if two or more masters attempt to control the bus simultaneously. This
feature provides the capability for complex applications with multi-processor control. It may
also be used for rapid testing and alignment of end products via external connections to an
assembly-line computer.
The M-bus module has the following key features:
 Compatible with I2C Bus Standard
 Multi-Master Operation
 Software Programmable for One of 32 Different Serial Clock Frequencies
 Software Selectable Acknowledge Bit
 Interrupt Driven Byte By Byte Data Transfer
 Arbitration Lost Interrupt with Automatic Mode Switching from Master to Slave
 Calling Address Identification Interrupt
 Start and Stop Signal Generation/Detection
 Repeated START Signal Generation
 Acknowledge Bit Generation/Detection
 Bus Busy Detection
A block diagram of the complete M-bus module is shown in 
Figure 7-1.Thi d
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ith F
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