Datasheet

Password
Some applications require protection against unauthor-
ized viewing of program code memory. For these applica-
tions, access to in-system programming, in-application
programming, or in-circuit debugging is prohibited until a
password has been supplied. The password is defined as
the 16 words of physical program memory at addresses
0010h–001Fh.
A single password lock (PWL) bit is implemented in
the device. When the PWL is set to 1 (power-on reset
default) and the contents of the memory at addresses
0010h–001Fh are any value other than all FFh or 00h, the
password is required to access the utility ROM, including
in-circuit debug and in-system programming routines that
allow reading or writing of internal memory. When PWL is
cleared to 0, these utilities are fully accessible without the
password. The password is automatically set to all ones
following a mass erase. Mass erase can be performed
without password match.
Detailed information regarding the password can be
found in the DS4830A User’s Guide.
Stack Memory
A 16-bit, 32-level internal stack provides storage for pro-
gram return addresses. The stack is used automatically
by the processor when the CALL, RET, and RETI instruc-
tions are executed and interrupts serviced. The stack can
also be used explicitly to store and retrieve data by using
the PUSH, POP, and POPI instructions.
On reset, the stack pointer, SP, initializes to the top of the
stack (1Fh). The CALL, PUSH, and interrupt-vectoring
operations increment SP, then store a value at the location
pointed to by SP. The RET, RETI, POP, and POPI opera-
tions retrieve the value at SP and then decrement SP.
Figure 6. Memory Map When Program Is Executing from Flash Memory
SYSTEM
REGISTERS
PERIPHERAL
REGISTERS
DP
32 x 16
STACK
M5
M4
M3
M2
M1
M0
5h
1Fh
00h
4h
3h
2h
1h
0h
FFFFh FFFFh FFFFh
8FFFh9FFFh8FFFh
7FFFh
0000h
0010h
001Fh
PASSWORD
0000h 0000h
4K x 16
UTILITY ROM
8K x 8
UTILITY ROM
4K x 16
UTILITY ROM
4K x 8
SRAM DATA
2K x 16
SRAM DATA
32K x 16
USER PROGRAM
FLASH MEMORY
8000h 8000h 8000h
0FFFh 07FFh
DPC
SP
IP
PFX
A
AP
Fh
00h 0Fh
00h 1Fh
Eh
Dh
Ch
Bh
9h
8h
PROGRAM
MEMORY SPACE
DATA MEMORY
(BYTE MODE)
DATA MEMORY
(WORD MODE)
DS4830A Optical Microcontroller
www.maximintegrated.com
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