t6020m ATMEL Corporation, t6020m Datasheet - Page 6

• Manufacturer Part Number: t6020m
• Description: Low-current Microcontroller For Watchdog Function
• Manufacturer: ATMEL Corporation

2.2
The core contains ROM, RAM, ALU, program counter,
RAM address registers, instruction decoder and interrupt
controller. The following sections describe each
functional block in more detail:
2.2.1
The program memory (ROM) is mask programmed with
the customer application program 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 2 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 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 4.
Look-up tables of constants can also be held in ROM and
are accessed via the MARC4’s built-in TABLE
instruction.
2.2.2
The T6020M contains 256 x 4-bit wide static random
access memory (RAM). It is used for the expression stack,
T6020M
6 (54)
Components of MARC4 Core
7FFFh
1FFh
000h
ROM
RAM
Zero page
(2 K x 8 bit)
ROM
Figure 4. ROM map of T6020M
the return stack and data memory 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 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 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 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.
1 E8h
1 E0h
0 20 h
0 00 h
1F8 h
1F0h
01 8 h
01 0 h
00 8h
Z ero
p ag e
1 E0 h
1 C0 h
1 00 h
0 C0 h
0 80 h
0 00 h
18 0h
14 0h
04 0h
00 8h
INT6
INT3
INT7
INT5
INT4
INT2
INT1
INT0
$RESET
$AUTOSLEEP
Rev. A3, 02-Apr-01
13391