Protocol For Termination Signals - Motorola MPC823e Reference Manual

13.4.9.4 PROTOCOL FOR TERMINATION SIGNALS. The transfer protocol was defined
to avoid electrical contention on signals that can be driven by various sources. To do that, a
slave must not drive signals associated with the data transfer until the address phase is
completed and it recognizes the address as its own. The slave must disconnect from signals
immediately after it has acknowledged the cycle and no later than the termination of the next
address phase cycle. This indicates that the termination signals must be connected to power
through a pull-up resistor to avoid a situation in which a master samples an undefined value
in any of these signals when no real slave is addressed. See Figure 13-24 and
Figure 13-25 for more information.
MPC823e
Figure 13-24. Termination Signals Protocol Basic Connection
CLKOUT
A[6:31]
RD/WR
TSIZ[0:1]
TS
DATA
TA,BI,TEA
Figure 13-25. Termination Signals Protocol Timing Diagram
MOTOROLA
EXTERNAL BUS
SLAVE 2
SLAVE 1 SLAVE 2
SLAVE 1
SLAVE 1 SLAVE 2
NEGATES
ALLOWED TO ALLOWED TO
ACKNOWLEDGE
DRIVE DRIVE
SIGNALS
ACKNOWLEDGE ACKNOWLEDGE
AND
SIGNALS SIGNALS
TURNS OFF
MPC823e REFERENCE MANUAL
External Bus Interface
SLAVE 1
ACKNOWLEDGE/TERMINATION
SIGNALS (TA, TEA, BI)
SLAVE 2
NEGATES
ACKNOWLEDGE
SIGNALS
AND
TURNS OFF
13-37