MPC563XM Reference Manual, Rev. 1
Freescale Semiconductor
369
Preliminary—Subject to Change Without Notice
13.5.2.9
Termination Signals Protocol
The termination signals protocol was defined in order to avoid electrical contention on lines that can be
driven by various sources. In order 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 acknowledges the cycle and not later than the termination of
the next address phase cycle.
For EBI-mastered non-chip-select accesses, the EBI requires assertion of TA from an external device to
signal that the bus cycle is complete. The EBI uses a latched version of TA (1 cycle delayed) for these
accesses to help make timing at high frequencies. This results in the EBI driving the address and control
signals 1 cycle longer than required, as seen in
. However, the DATA does not need to be held
1 cycle longer by the slave, because the EBI latches DATA every cycle during non-chip-select accesses.
During these accesses, the EBI does not drive the TA signal, leaving it up to an external device (or weak
internal pullup) to drive TA.
For EBI-mastered chip-select accesses, when the SETA bit is 0, the EBI drives TA the entire cycle,
asserting according to internal wait state counters to terminate the cycle. When the SETA bit is 1, the EBI
samples the TA for the entire cycle. During idle periods on the external bus, the EBI drives TA negated as
long as it is granted the bus; when it no longer owns the bus, it lets go of TA. When an external master does
a transaction to internal address space, the EBI only drives TA for the cycle it asserts TA to return data and
for 1 cycle afterwards to ensure fast negation.
If no device responds by asserting TA within the programmed timeout period (BMT in EBI_BMCR) after
the EBI initiates the bus cycle, the internal Bus Monitor (if enabled) asserts TEA to terminate the cycle.
An external device may also drive TEA when it detects an error on an external transaction. TEA assertion
causes the cycle to terminate and the processor to enter exception processing for the error condition. To
properly control termination of a bus cycle for a bus error with external circuitry, TEA must be asserted at
the same time or before (external) TA is asserted. TEA must be negated before the second rising edge after
it was sampled asserted in order to avoid the detection of an error for the following bus cycle initiated.
TEA is only driven by the EBI during the cycle where the EBI is asserting TEA and the cycle immediately
following this assertion (for fast negation). During all other cycles, the EBI relies on a weak internal pullup
to hold TEA negated. This allows an external device to assert TEA when it needs to indicate an error.
External devices must follow the same protocol as the EBI, only driving TEA during the assertion cycle
and 1 cycle afterwards for negation.
NOTE
In the case where an external master asserts TEA to timeout a transaction to
an internal address on this MCU, the EBI has no way to terminate the
transfer internally. Therefore, any subsequent TS assertions by the external
master are ignored by the EBI until the original transfer has completed
internally and the EBI has returned to an idle state. The expectation is that
the internal slaves will always respond with either valid data or an error
indication within a reasonable period of time to avoid hanging the system.
When TEA is asserted from an external source, the EBI uses a latched version of TEA (1 cycle delayed)
to help make timing at high frequencies. This means that for any accesses where the EBI drives TA
(chip-select accesses with SETA=0 and external master accesses to EBI), a TEA assertion that occurs 1