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External Bus Interface (EBI)
MPC5644A Microcontroller Reference Manual, Rev. 6
Freescale Semiconductor
325
shows an example of the termination signals protocol for back-to-back reads to two different
slave devices who properly “take turns” driving the termination signals. This assumes a system using slave
devices that drive termination signals.
Figure 14-33. Termination Signals Protocol Timing Diagram
14.5.2.9
Non-chip-select burst in 16-bit data bus mode
The timing diagrams in this section apply only to the special case of a non-chip-select 32-bit access in
16-bit data bus mode (DBM=1 in EBI_MCR).
For this case, a special 2-beat burst protocol is used for reads and writes, so that a slave device (using the
same EBI) can internally generate one 32-bit read or write access (thus 32-bit coherent), as opposed to two
separate 16-bit accesses.
Asserted
X
Transfer Error Termination
Negated
Asserted
Normal Transfer Termination
1
Latched version (1 cycle delayed) used for externally
driven TEA and TA.
Table 14-18. Termination Signals Protocol (continued)
TEA
1
TA
1
Action
The EBI drives address and control signals an extra cycle because it uses a latched version of TA
*
This is the earliest that the EBI can start another transfer, in the case of continuing a set of small accesses.
For all other cases, an extra cycle is needed before the EBI can start another TS.
**
CLKOUT
BB
TS
DATA[0:31]
TA, TEA
ADDR[3:31]
RD_WR
Slave 1
Slave 2
*
*
**
(1 cycle delayed) to terminate the cycle. An external master is not required to do this.
Slave 1
negates
acknowledge
signals and
turns off
Slave 2
negates
acknowledge
signals and
turns off
Slave 2
allowed to
drive
acknowledge
signals
Slave 1
allowed to
drive
acknowledge
signals
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