MPC5553/MPC5554 Microcontroller Reference Manual, Rev. 5
12-26
Freescale Semiconductor
12.4.1.18 Compatible with MPC5xx External Bus
(with Some Limitations)
The EBI is compatible with the external bus of the MPC5xx parts, meaning that it supports most devices
supported by the MPC5xx family of parts. However, there are some differences between this EBI and that
of the MPC5xx parts that the user needs to be aware of before assuming that an MPC5xx-compatible
device works with this EBI. See
Section 12.5.6, “Summary of Differences from MPC5xx
,” for details.
NOTE
Due to testing and complexity concerns, multi-master (or master/slave)
operation between an MPC55xx MCU and MPC5xx is not guaranteed.
12.4.2
External Bus Operations
The following sections provide a functional description of the external bus, the bus cycles provided for
data transfer operations, bus arbitration, and error conditions.
12.4.2.1
External Clocking
The CLKOUT signal sets the frequency of operation for the bus interface directly. Internally, the MCU
uses a phase-locked loop (PLL) circuit to generate a master clock for all of the MCU circuitry (including
the EBI) which is phase-locked to the CLKOUT signal. In general, all signals for the EBI are specified
with respect to the rising-edge of the CLKOUT signal, and they are guaranteed to be sampled as inputs or
changed as outputs with respect to that edge.
12.4.2.2
Reset
Upon detection of internal reset, the EBI immediately terminates all transactions.
12.4.2.3
Basic Transfer Protocol
The basic transfer protocol defines the sequence of actions that must occur on the external bus to perform
a complete bus transaction. A simplified scheme of the basic transfer protocol is shown in
.
Figure 12-8. Basic Transfer Protocol
The arbitration phase is where bus ownership is requested and granted. This phase is not needed in single
master mode because the EBI is the permanent bus owner in this mode. Arbitration is discussed in detail
in
Section 12.4.2.8, “Arbitration
.”
The address transfer phase specifies the address for the transaction and the transfer attributes that describe
the transaction. The signals related to the address transfer phase are TS, ADDR, CS[0:3], RD_WR,
TSIZ[0:1], and BDIP. The address and its related signals (with the exception of TS, BDIP) are driven on
the bus with the assertion of the TS signal, and kept valid until the bus master receives TA asserted (the
EBI holds them one cycle beyond TA for writes and external TA accesses). Note that for writes with
internal TA, RD_WR is not held one cycle past TA.
Arbitration
Address Transfer
Data Transfer
Termination
Содержание MPC5553
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