ATAM862 datasheet(16/110 Pages) ATMEL

16 / 110 page

4554E–4BMCU–05/06

ATAM862-3

16.1

Program Memory

The program memory (EEPROM) is programmable with the customer application program dur-

ing the fabrication of the microcontroller. The EEPROM is addressed by a 12-bit wide program

counter, thus predefining a maximum program bank size of 4-Kbytes. The lowest user program

memory address segment is taken up by a 512 bytes Zero page which contains predefined start

addresses for interrupt service routines and special subroutines accessible with single byte

instructions (SCALL).

The corresponding memory map is shown in Figure 16-1. Look-up tables of constants can also

be held in ROM and are accessed via the microcontrollers’ built-in table instruction.

Figure 16-1. ROM Map of the Microcontroller Block

16.2

RAM

The microcontroller block contains a 256 x 4-bit wide static random access memory (RAM),

which is used for the expression stack. The return stack and data memory are used for variables

and arrays. The RAM is addressed by any of the four 8-bit wide RAM address registers SP, RP,

X and Y.

16.2.1

Expression Stack

The 4-bit wide expression stack is addressed with the expression stack pointer (SP). All arith-

metic, I/O and memory reference operations take their operands, and return their results to the

expression stack. The microcontroller performs the operations with the top of stack items (TOS

and TOS-1). The TOS register contains the top element of the expression stack and works in the

same way as an accumulator. This stack is also used for passing parameters between subrou-

tines and as a scratch pad area for temporary storage of data.

16.2.2

Return Stack

The 12-bit wide return stack is addressed by the return stack pointer (RP). It is used for storing

return addresses of subroutines, interrupt routines and for keeping loop index counts. The return

stack can also be used as a temporary storage area.

The microcontroller instruction set supports the exchange of data between the top elements of

the expression stack and the return stack. The two stacks within the RAM have a user definable

location and maximum depth.

EEPROM

(4 K x 8 bit)

Zero page

FFFh

7FFh

1FFh

000h

1F0h

1F8 h

010 h

018 h

000h

008h

020h

1E8h

1E0h

140h

180h

040h

0C 0h

008h

$AUTOSLEEP

$RESET

INT0

INT1

INT2

INT3

INT4

INT5

INT6

INT7

1E0h

1C 0h

100h

080h

page

000h

ATAM862 Datasheet(PDF) 16 Page - ATMEL Corporation

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