Datasheet

28
2549O–AVR–05/12
ATmega640/1280/1281/2560/2561
9. 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)
9.1 Overview
W hen the eXternal MEMory (XMEM) is enabled, address space outside the internal SRAM
becomes available using the dedicated External Memory pins (see Figure 1-3 on page 4, Table
13-3 on page 78, Table 13-9 on page 82, and Table 13-21 on page 90). The memory configura-
tion is shown in Figure 9-1.
Figure 9-1. External Memory with Sector Select
Memory Configuration A
0x0000
0x21FF
External Memory
(0 - 60K x 8)
0xFFFF
Internal memory
SRL[2..0]
SRW11
SRW10
SRW01
SRW00
Lower sector
Upper sector
0x2200