Datasheet

24
ATmega8515(L)
2512G–AVR–03/05
External Memory
Interface
With all the features the External Memory Interface provides, it is well suited to operate
as an interface to memory devices such as external SRAM and Flash, and peripherals
such as LCD-display, A/D, and D/A. The main features are:
•
Four Different Wait State Settings (Including No wait State)
• Independent Wait State Setting for Different External Memory Sectors (Configurable
Sector Size)
• The Number of Bits Dedicated to Address High Byte is Selectable
• Bus Keepers on Data Lines to Minimize Current Consumption (Optional)
Overview When the eXternal MEMory (XMEM) is enabled, address space outside the internal
SRAM becomes available using the dedicated external memory pins (see Figure 1 on
page 2, Table 26 on page 65, Table 32 on page 69, and Table 38 on page 73). The
memory configuration is shown in Figure 11.
Figure 11. External Memory with Sector Select
Using the External Memory
Interface
The interface consists of:
• AD7:0: Multiplexed low-order address bus and data bus
• A15:8: High-order address bus (configurable number of bits)
• ALE: Address latch enable
•RD
: Read strobe
•WR
: Write strobe
0x0000
0x25F
External Memory
(0-64K x 8)
0xFFFF
Internal Memory
SRL[2..0]
SRW11
SRW10
SRW01
SRW00
Lower Sector
Upper Sector
0x260