External Bus Interface
MPC561/MPC563 Reference Manual, Rev. 1.2
Freescale Semiconductor
9-45
9.5.11
Bus Exception Control Cycles
The MPC561/MPC563 bus architecture requires assertion of TA from an external device to signal that the
bus cycle is complete. TA is not asserted in the following cases:
•
The external device does not respond
•
Various other application-dependent errors occur
External circuitry can provide TEA when no device responds by asserting TA within an appropriate period
of time after the MPC561/MPC563 initiates the bus cycle (it can be the internal bus monitor). This allows
the cycle to terminate and the processor to enter exception-processing for the error condition (each one of
the internal masters causes an internal interrupt under this situation). To properly control termination of a
bus cycle for a bus error, TEA must be asserted at the same time or before TA is asserted. TEA should be
negated before the second rising edge after it was sampled as asserted to avoid the detection of an error for
the next initiated bus cycle. TEA is an open drain pin that allows the “wired-or” of any different sources
of error generation.
9.5.11.1
Retrying a Bus Cycle
When an external device asserts the RETRY signal during a bus cycle, the MPC561/MPC563 enters a
sequence in which it terminates the current transaction, relinquishes the ownership of the bus, and retries
the cycle using the same address, address attributes, and data (in the case of a write cycle).
illustrates the behavior of the MPC561/MPC563 when the RETRY signal is detected as a
termination of a transfer. As seen in this figure, in the case when the internal arbiter
is enabled, the
MPC561/MPC563 negates BB and asserts BG in the clock cycle following the retry detection. This allows
any external master to gain bus ownership. In the next clock cycle, a normal arbitration procedure occurs
again. As shown in the figure, the external master did not use the bus, so the MPC561/MPC563 initiates a
new transfer with the same address and attributes as before.
, the same situation is shown except that the MPC561/MPC563 is working with an external
arbiter. In this case, in the clock cycle after the RETRY signal is detected asserted, BR is negated together
with BB. One clock cycle later, the normal arbitration procedure occurs again.
Summary of Contents for MPC561
Page 84: ...MPC561 MPC563 Reference Manual Rev 1 2 lxxxiv Freescale Semiconductor...
Page 144: ...Signal Descriptions MPC561 MPC563 Reference Manual Rev 1 2 2 46 Freescale Semiconductor...
Page 206: ...Central Processing Unit MPC561 MPC563 Reference Manual Rev 1 2 3 62 Freescale Semiconductor...
Page 302: ...Reset MPC561 MPC563 Reference Manual Rev 1 2 7 14 Freescale Semiconductor...
Page 854: ...Time Processor Unit 3 MPC561 MPC563 Reference Manual Rev 1 2 19 24 Freescale Semiconductor...
Page 968: ...Development Support MPC561 MPC563 Reference Manual Rev 1 2 23 54 Freescale Semiconductor...
Page 1144: ...Internal Memory Map MPC561 MPC563 Reference Manual Rev 1 2 B 34 Freescale Semiconductor...
Page 1212: ...TPU3 ROM Functions MPC561 MPC563 Reference Manual Rev 1 2 D 60 Freescale Semiconductor...
Page 1216: ...Memory Access Timing MPC561 MPC563 Reference Manual Rev 1 2 E 4 Freescale Semiconductor...