External Bus Interface (EBI)
30-50
Freescale Semiconductor
PXR40 Microcontroller Reference Manual, Rev. 1
•
Copy the code that is doing the register writes (plus a return branch) to internal SRAM
•
Branch to internal SRAM to run this code, ending with a branch back to external flash
30.5.2
Running with SDR (Single Data Rate) Burst Memories
This includes FLASH and SRAM memories with a compatible burst interface. D_BDIP is required only
for some SDR memories.
shows a block diagram of an MCU connected to a 32-bit SDR burst
memory.
Figure 30-38. MCU Connected to SDR Burst Memory
Refer to
for an example of the timing of a typical Burst Read operation to an SDR burst
memory. Refer to
for an example of the timing of a typical Single Write operation to SDR
memory.
30.5.3
Running with Asynchronous Memories
The EBI also supports asynchronous memories. In this case, the D_CLKOUT, D_TS, and D_BDIP pins
are not used by the memory and bursting is not supported. However, the EBI still drives these outputs, and
always drives and latches all signals at posedge D_CLKOUT (i.e., there is no “asynchronous mode” for
the EBI). The data timing is controlled by setting the SCY bits in the appropriate Option Register to the
proper number of wait states to work with the access time of the asynchronous memory, just as done for a
synchronous memory.
30.5.3.1
Example Wait State Calculation
This example applies to any chip-select memory, synchronous or asynchronous.
As an example, say we have a memory with 50ns access time, and we are running the external bus
@ 66 MHz (D_CLKOUT period: 15.2ns). Assume the input data spec for the MCU is 4ns.
number of wait states = (access time) / (D_CLKOUT period) + (0 or 1) (depending on setup time)
D_CLKOUT
CS0
D_TS
D_ADD[9:30]
D_BDIP
D_OE
MCU
CK
CE
ADV
BAA*
WE**
A[0:21]
D[0:31]
OE
SDR Burstable
Flash or SRAM
* May or may not be connected, depending on the memory used.
Flash memories typically use one WE signal as shown, RAMs use 2 or 4 (16-bit or 32-bit).
**
D_ADD_DAT[0:31]
D_WE0
Summary of Contents for PXR4030
Page 1: ...PXR40 Microcontroller Reference Manual Devices Supported PXR4030 PXR4040 PXR40RM Rev 1 06 2011...
Page 30: ...PXR40 Microcontroller Reference Manual Rev 1 Freescale Semiconductor xxx...
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Page 120: ...Signal Descriptions 3 54 Freescale Semiconductor PXR40 Microcontroller Reference Manual Rev 1...
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