External Bus Interface (EBI)
Freescale Semiconductor
30-21
PXR40 Microcontroller Reference Manual, Rev. 1
30.4.1.14 Optional Automatic D_CLKOUT Gating
The EBI has the ability to hold the external D_CLKOUT pin high when the EBI’s internal master state
machine is idle and no requests are pending. The EBI outputs a signal to the pads logic in the MCU to
disable D_CLKOUT. This feature is disabled out of reset, and can be enabled or disabled by the ACGE
bit in the EBI_MCR.
NOTE
This feature must be disabled for multi-master systems. In those cases, one
master is getting its clock source from the other master and needs it to stay
valid continuously.
30.4.1.15 Misaligned Access Support
The EBI has limited misaligned access support. Misaligned non-burst chip-select transfers from internal
masters are supported. The EBI aligns the accesses when it sends them out to the external bus (splitting
them into multiple aligned accesses if necessary), so that external devices are not required to support
misaligned accesses. Burst accesses (internal master) must match the internal bus size (64-bit aligned). See
Section 30.4.2.11, Misaligned Access Support
, for more details.
30.4.1.16 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 30.5.5, Summary of Differences from MPC5xx
,
for details.
NOTE
Due to testing and complexity concerns, multi-master (or master/slave)
operation between an eSys MCU and MPC5xx is not guaranteed.
30.4.2
External Bus Operations
The following sections provide a functional description of the external bus, the bus cycles provided for
data transfer operations, and error conditions.
30.4.2.1
External Clocking
Possible division factors for D_CLKOUT: 1, 2, and 4.
The D_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 D_CLKOUT signal. In general, all signals for the EBI are specified
with respect to the rising-edge of the D_CLKOUT signal, and they are guaranteed to be sampled as inputs
or changed as outputs with respect to that edge.
Summary of Contents for PXR4030
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