Bus Busy (Bb) - Freescale Semiconductor MPC850 User Manual

Bus Operations

13.4.6.3 Bus Busy (BB)

BB indicates that the current master is using the bus. New masters should not begin a
transfer until BB is deasserted. The bus master should not relinquish or negate BB until it
completes its transfer. To avoid contention on BB, masters should three-state BB when it
gets a logical 1 value. This situation implies an external pull-up resistor is needed to ensure
that a master that acquires the bus can recognize the negation of BB, regardless of how
many cycles have passed since the previous master relinquished the bus. See Figure 13-22.
MPC850
Figure 13-22. Bus Busy (BB) and Transfer Start (TS) Connection Example
Figure 13-23 shows an example bus arbitration between two contending masters.
External Bus
TS
BB
Slave 2
MPC850 Family User's Manual
Master