DS80CH11 Datasheet, PDF (43/88 Pages) Dallas Semiconductor – System Energy Manager

DS80CH11
6.3.5 Bus Monitor Mode Operation
The bus monitor mode is provided to allow the SEM to
“listen” as a third party to conversations between exter-
nal master and slave devices. This mode can be useful
for diagnostic purposes, or to help the system recover
from a detected error condition.
When the BMMx bit is set to 1, bus monitoring is
enabled. In this mode the port will generate an interrupt
for every action on the bus even when it is not operating
as a master or being addressed as a slave. As a result,
when a transfer takes place between an external master
and slave, the port will be notified of a transmitted
START condition, will receive the subsequent address
and data bytes on the bus, and will finally be notified of a
transmitted STOP condition.
If the SEM is receiving a transfer between an external
master and an external slave device, the timing is nearly
identical to that for Slave Receive operation as shown in
Figure 6–6. The exceptions to this timing are summa-
rized as follows: 1) An additional interrupt will be gener-
ated when a Receive START condition is detected as
indicated by RSTAx = 1. This will inform the firmware of
the start of a message and allow it to identify the next
byte as an address. 2) A positive acknowledge pulse
will never be generated. 3) SCLx will never be held low
to prevent data in the receive buffer from being overwrit-
ten. Other than these differences bytes are received
and all other status is flagged as described for Slave
Receiver operation.
When BMMx = 1 and the SEM is operating as a master
or is being addressed as a slave, the Master Transmit,
Master Receive, Slave Transmit, and Slave Receive
modes will all operate exactly as documented above
with the exception that RSTAx becomes an additional
interrupt flag that is set whenever a START condition is
detected on the bus.
When BMMx = 0, bus monitoring is disabled and inter-
rupt flags are only generated when the port is operating
as a master or being addressed as a slave device.
Transfers between external devices are ignored.
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