ATA6020N ATMEL Corporation, ATA6020N Datasheet - Page 5

• Manufacturer Part Number: ATA6020N
• Description: Low-current Microcontroller For Watchdog Function
• Manufacturer: ATMEL Corporation

4.1.2
4.1.2.1
4.1.2.2
4.1.3
4708D–4BMCU–09/05
RAM
Registers
Expression Stack
Return Stack
The ATA6020N contains 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.
Figure 4-3.
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 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 subrou-
tines and as a scratch pad area for temporary storage of data.
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.
The MARC4 controller has seven programmable registers and one condition code register. They
are shown in the following programming model.
RAM Map
SP
RP
X
Y
FCh
04h
00h
Autosleep
TOS-1
(256 x 4-bit)
RAM
FFh
07h
03h
Expression
stack
Return
stack
Global
variables
Global
v
variables
Expression stack
11
Return stack
3
TOS-1
TOS-2
4-bit
TOS
12-bit
ATA6020N
0
SP
0
RP
5