AN2408 Freescale Semiconductor / Motorola, AN2408 Datasheet - Page 17

• Manufacturer Part Number: AN2408
• Description: Examples of HCS12 External Bus Design A Companion Note to AN2287/D
• Manufacturer: Freescale Semiconductor / Motorola

Example #7 — Word-Wide External Device Interface – 100BASE-T Ethernet
Figure 18
expanded wide mode in order to support word (x16) access to the external device.
Comments:
Freescale Semiconductor
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Only the bus interface to the external device is shown. Additional external devices are required to
implement a fully functional Ethernet system. Please refer to the external device’s specifications
for these details.
The data bus from the MCU is flipped (low byte to high byte) to accommodate the interface to big
Endian data bus of the external device. While this is not absolutely necessary, it will make the
software interface cleaner.
This external device has internal address latching to interface to a multiplexed bus. The address
latches are used in this design to delay the addresses in order to meet the setup/hold time
requirements of the external device’s internal address latch.
Memory Map
00
10
demonstrates the interface to a 16-bit Ethernet device to provide word access. It uses
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External FLASH
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Examples of HCS12 External Bus Design, Rev. 2
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Figure 17. Memory Map of
0A
1A
0B
1B
Example #7 — Word-Wide External Device Interface – 100BASE-T Ethernet
0C
1C
0D
1D
0E
1E
0F
1F
0000
FFFF
3E
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3F
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Figure 16
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Internal Flash
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3A
3B
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3D
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3F
PPAGE
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