ATMEGA8515L8AU

Manufacturer Part NumberATMEGA8515L8AU
DescriptionTQFP44
ManufacturerATMEL Corporation
ATMEGA8515L8AU datasheet
 

Specifications of ATMEGA8515L8AU

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Special Function IO Register –
SFIOR
Using all Locations of
External Memory Smaller than
64 KB
2512J–AVR–10/06
Bit
7
6
5
XMBK
XMM2
Read/Write
R/W
R/W
R/W
Initial Value
0
0
0
• Bit 6 – XMBK: External Memory Bus Keeper Enable
Writing XMBK to one enables the Bus Keeper on the AD7:0 lines. When the Bus Keeper
is enabled, AD7:0 will keep the last driven value on the lines even if the XMEM interface
has tri-stated the lines. Writing XMBK to zero disables the Bus Keeper. XMBK is not
qualified with SRE, so even if the XMEM interface is disabled, the Bus Keepers are still
activated as long as XMBK is one.
• Bit 5..3 – XMM2, XMM1, XMM0: External Memory High Mask
When the External Memory is enabled, all Port C pins are used for the high address
byte by default. If the full 64,928 bytes address space is not required to access the
External Memory, some, or all, Port C pins can be released for normal Port Pin function
as described in Table 4. As described in “Using all 64KB Locations of External Memory”
on page 33, it is possible to use the XMMn bits to access all 64KB locations of the Exter-
nal Memory.
Table 4. Port C Pins Released as Normal Port Pins when the External Memory is
Enabled
XMM2
XMM1
XMM0
# Bits for External Memory Address
0
0
0
8 (Full 64,928 Bytes Space)
0
0
1
7
0
1
0
6
0
1
1
5
1
0
0
4
1
0
1
3
1
1
0
2
1
1
1
No Address High bits
Since the external memory is mapped after the internal memory as shown in Figure 11,
the external memory is not addressed when addressing the first 608 bytes of data
space. It may appear that the first 608 bytes of the external memory are inaccessible
(external memory addresses 0x0000 to 0x025F). However, when connecting an exter-
nal memory smaller than 64 KB, for example 32 KB, these locations are easily accessed
simply by addressing from address 0x8000 to 0x825F. Since the External Memory
Address bit A15 is not connected to the external memory, addresses 0x8000 to 0x825F
will appear as addresses 0x0000 to 0x025F for the external memory. Addressing above
address 0x825F is not recommended, since this will address an external memory loca-
tion that is already accessed by another (lower) address. To the Application software,
the external 32 KB memory will appear as one linear 32 KB address space from 0x0260
to 0x825F. This is illustrated in Figure 17.
ATmega8515(L)
4
3
2
1
XMM1
XMM0
PUD
PSR10
R/W
R/W
R/W
R/W
0
0
0
0
Released Port Pins
None
PC7
PC7 - PC6
PC7 - PC5
PC7 - PC4
PC7 - PC3
PC7 - PC2
Full Port C
0
SFIOR
R/W
0
31