Applications Information
MOTOROLA
MC68307 USER’S MANUAL
10-13
valid data and initiate the next byte receive. Again, the software protocol between M-bus
master and slave determines the use of acknowledges.
10.3.4 Description of Setup
The hardware consists of two identical MC68307 systems connected together via the M-bus
as shown in
Figure 10-2. Both systems have the MC68307 processor core executing
instructions prefetched from its own ROM.
Figure 10-2. Hardware Setup
Each MC68307 system has 128 Kbytes EPROM and 128 Kbytes SRAM and runs a debug
monitor. A complete description of the system hardware is provided in AN490, titled “Multiple
Bus Interfaces using the MC68307.
Using the monitor's download facility, an M-bus control program is downloaded into the
SRAM of each board. The code allows one system to control its M-bus module as a master,
while the other implements an M-bus slave. Together, the two software programs allow the
MC68307 M-bus master to write data to the MC68307 M-bus slave and later read it back for
verification.
10.3.5 Software Flow
The MC68307 master M-bus controls the number of blocks transferred via START and
STOP conditions. In this example, there are only two communication blocks, one transmit-
ting data to the slave (master transmit block), and one receiving data back from the slave
for verification (master receive block). The master/slave responsibilities during the master
On these diagrams, note that for a given transfer byte, the end-of-byte interrupts on the mas-
ter and slave occur at around the same time. The built-in M-bus transfer mechanism means
it does not matter in which order they are serviced. The master and slave interrupt service
poses. The interrupt handlers are shown such that the data flow is always from transmitter
to receiver, although, it should be understood that the master and slave interrupt handlers
are happening at the same time, as are the transmit and receive of a particular byte between
the two systems.
MC68307
SYSTEM
SCL
SDA
MASTER
M-BUS
MC68307
SYSTEM
SCL
SDA
SLAVE
M-BUS
5V
2.2K