W90N745CD/W90N745CDG
6.3 External Bus Interface
6.3.1 EBI Overview
W90N745 supports External Bus Interface (EBI), which controls the access to the external memory
(ROM/FLASH, SDRAM) and External I/O devices. The EBI has seven chip selects to select one
ROM/FLASH bank, two SDRAM banks, and four External I/O banks.The address bus is 21 bits. It
supports 8-bit, 16-bit external data bus width for each bank.
The EBI has the following functions：
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y
y
y
y
SDRAM controller
EBI control register
ROM/FLASH interface
External I/O interface
External bus mastership
6.3.2 SDRAM Controller
The SDRAM controller module within W90N745 contains configuration registers 、 timing control
registers、common control register and other logic to provide 8、16 bits SDRAM interface with a single
8、16 bits SDRAM device or two 8-bit devices wired to give a 16-bit data path. The maximum size of
each bank is 64M bytes, and maximum memory size can span up to 128MB.
The SDRAM controller has the following features：
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y
y
y
y
y
y
y
y
Supports up to 2 external SDRAM banks
Maximum size of each bank is 64M bytes
8、16-bit data interface
Programmable CAS Latency： 1、2 and 3
Fixed Burst Length： 1
Sequential burst type
Auto Refresh Mode and Self Refresh Mode
Adjustable Refresh Rate
Power up sequence
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