參數(shù)資料
型號(hào)： MR83C154XXX-25P883
廠商： ATMEL CORP
元件分類(lèi)： 微控制器/微處理器
英文描述： 8-BIT, MROM, 25 MHz, MICROCONTROLLER, CQCC44
封裝： LCC-44
文件頁(yè)數(shù)： 63/80頁(yè)
文件大?。?/td> 5152K
代理商： MR83C154XXX-25P883
263
XMEGA A [MANUAL]
8077I–AVR–11/2012
24.
EBI – External Bus Interface
24.1
Features
Supports SRAM up to:
– 512KB using 2-port EBI
– 16MB using 3-port EBI
Supports SDRAM up to:
– 128Mb using 3-port EBI
Four software configurable chip selects
Software configurable wait state insertion
Can run from the 2x peripheral clock frequency for fast access
24.2
Overview
The External Bus Interface (EBI) is used to connect external peripherals and memory for access through the data
memory space. When the EBI is enabled, data address space outside the internal SRAM becomes available using
dedicated EBI pins.
The EBI can interface external SRAM, SDRAM, and peripherals, such as LCD displays and other memory mapped
devices.
The address space for the external memory is selectable from 256 bytes (8-bit) up to 16MB (24-bit). Various multiplexing
modes for address and data lines can be selected for optimal use of pins when more or fewer pins are available for the
EBI. The complete memory will be mapped into one linear data address space continuing from the end of the internal
SRAM. Refer to “Data Memory” on page 21 for details.
The EBI has four chip selects, each with separate configuration. Each can be configured for SRAM, SRAM low pin count
(LPC), or SDRAM.
The EBI is clocked from the fast, 2x peripheral clock, running up to two times faster than the CPU.
Four-bit and eight-bit SDRAM are supported, and SDRAM configurations, such as CAS latency and refresh rate, are
configurable in software.
For more details on SRAM and SDRAM, and on how these memory types are organized and work, refer to SRAM and
SDRAM-specific documentation and datasheets. This section only contains EBI-specific details.
24.3
Chip Select
The EBI module has four chip select lines (CS0 to CS3), which can be associated with separate address ranges. The
chip selects control which memory or memory mapped external hardware is accessed when a given memory address is
issued on the EBI. Each chip select has separate configuration, and can be configured for SRAM or SRAM low pin count
(LPC). Chip select 3 can also be configured for SDRAM.
Each chip select has a configurable base address and address size, which are used to determine the data memory
address space associated with each chip select.
24.3.1 Base Address
The base address assigned to a chip select is the lowest address in the address space, and determines the first location
in data memory space where the connected memory hardware can be accessed. The base address associated with
each chip select must be on a 4KB boundary.
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