AT90S8515

Manufacturer Part NumberAT90S8515
Description8-bit microcontroller with 8K bytes in-system programmable flash, 2.7-6.0V
ManufacturerATMEL Corporation
AT90S8515 datasheet
 
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Page 12/112:

SRAM Data Memory Internal and External

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SRAM Data Memory –
Internal and External
AT90S8515
12
Figure 8 shows how the AT90S8515 SRAM memory is organized.
Figure 8. SRAM Organization
Register File
R0
R1
R2
R29
R30
R31
I/O Registers
$00
$01
$02
$3D
$3E
$3F
The lower 608 data memory locations address the Register file, the I/O memory and the
internal data SRAM. The first 96 locations address the Register file + I/O memory, and
the next 512 locations address the internal data SRAM. An optional external data SRAM
can be placed in the same SRAM memory space. This SRAM will occupy the location
following the internal SRAM and up to as much as 64K - 1, depending on SRAM size.
When the addresses accessing the data memory space exceed the internal data SRAM
locations, the external data SRAM is accessed using the same instructions as for the
internal data SRAM access. When the internal data space is accessed, the read and
write strobe pins (RD and WR) are inactive during the whole access cycle. External
SRAM operation is enabled by setting the SRE bit in the MCUCR register. See page 29
for details.
Accessing external SRAM takes one additional clock cycle per byte compared to access
of the internal SRAM. This means that the commands LD, ST, LDS, STS, PUSH and
POP take one additional clock cycle. If the stack is placed in external SRAM, interrupts,
subroutine calls and returns take two clock cycles extra because the 2-byte program
counter is pushed and popped. When external SRAM interface is used with wait state,
Data Address Space
$0000
$0001
$0002
$001D
$001E
$001F
$0020
$0021
$0022
$005D
$005E
$005F
Internal SRAM
$0060
$0061
$025E
$025F
External SRAM
$0260
$0261
$FFFE
$FFFF
0841G–09/01