ATAR092 datasheet(4/100 Pages) ATMEL

4 / 100 page

ATAR092/ATAR892

4535C–4BMCU–02/04

Components of MARC4

Core

The core contains ROM, RAM, ALU, program counter, RAM address registers, instruc-

tion decoder and interrupt controller. The following sections describe each functional

block in more detail.

ROM

The program memory (ROM) is mask programmed with the customer application pro-

gram during the fabrication of the microcontroller. The ROM is addressed by a 12-bit

wide program counter, thus predefining a maximum program bank size of 4 Kbytes. An

additional 1 Kbyte of ROM exists which is reserved for quality control self-test software

The lowest user ROM address segment is taken up by a 512-byte zero page which con-

tains predefined start addresses for interrupt service routines and special subroutines

accessible with single byte instructions (SCALL).

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 MARC4’s built-in table instruction.

Figure 4. ROM Map

RAM

The ATAR092 and ATAR892 contain 256 x 4-bit wide static random access memory

(RAM). It is used for the expression stack, the return stack and data memory for vari-

ables 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 from, and return

their results to the expression stack. The MARC4 performs the operations with the top of

stack items (TOS and TOS-1). The TOS register contains the top element of the expres-

sion 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 stor-

age 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 MARC4 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.

ROM

(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

0C0h

008h

$AUTOSLEEP

$RESET

INT0

INT1

INT2

INT3

INT4

INT5

INT6

INT7

1E0h

1C0h

100h

080h

page

000h

Zero

ATAR092 Datasheet(PDF) 4 Page - ATMEL Corporation

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