Rainbow Electronics W90N740 - Manual (Page 39)

W90N740
Publication Release Date: November 26, 2004
- 35 - Revision A4
RESET [0] ： Reset
This is a software reset control bit. Set logic 1 to generate an internal reset pulse. This bit is auto-clear to
logic 0 at the end of the reset pulse.
7.3 External Bus Interface (EBI)
7.3.1 EBI Overview
External Bus Interface (EBI) controls the access to the external memory (ROM/SRAM/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 and 25-bit address bus. It supports 8-bit, 16-bit, and 32-bit external
data bus width for each bank.
The Features of the EBI：
z External I/O Control with 8/16/32 bit external data bus
z Cost-effective memory-to-peripheral DMA interface
z SDRAM Controller supports up to 2 external SDRAM & the maximum size of each device is 32MB
z ROM/FLASH & External I/O interface
z Support for PCMCIA 16-bit PC Card devices
7.3.2 SDRAM Controller
The W90N740’s SDRAM Controller contains configuration registers, timing control registers, common
control register and other logic. The SDRAM Controller provides 8/16/32 bits SDRAM interface with a
single 8/16/32 bits SDRAM device or two 8-bit devices wired to give a 16-bit data path or two 16-bit
devices wired to give a 32-bit data path. The maximum memory size of each bank is 32MB(Mbytes). One
of two banks can be connected to the SDRAM interface, so the maximum memory can be up to 64MB.
The Features of the SDRAM Controller：
• 8/16/32-bit data interface
• Supports up to 2 external SDRAM devices and Maximum size of each device is 32MB
• Programmable CAS Latency： 1、2 and 3
• Fixed Burst Length： 1
• Sequential burst type
• Write Burst Length mode is Burst
• Auto Refresh Mode and Self Refresh Mode
• Adjustable Refresh Rate
• Power up sequence