T48C862-R3 datasheet(15/107 Pages) ATMEL

15 / 107 page

T48C862-R3

4554A–4BMCU–02/03

The corresponding memory map is shown in Figure 4. Look-up tables of constants can

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

Figure 10. ROM Map of the Microcontroller Block

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.

Expression Stack

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

arithmetic, 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 subroutines and as a scratch pad area for temporary

storage of data.

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 ele-

ments 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

1F8h

010h

018h

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

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