ARM Memory Addresses

I am running into problems when trying to write to memory addresses on an older LPC2148 microntroller. I have tried writing to several different parts of the memory map (Section 6.4) from http://www.keil.com/dd/docs/datashts/philips/lpc2141_42_44_46_48.pdf such as on-board non-volatile, static, etc. I have also tried STMDB to the stack (0x40000000?) but the debugger sends me to the PrefetchAbort (expected if memory is non-accessible).

What am I not understanding about the memory map?

Are there global default values? I can't work with any of the ones declared in the startup.

How can I write specifically to the stack? (using STMFD or STMDB/STMIA)?

[STACK ATTEMPT] * with same startup file as below - Full Descending Stack

LDR r1, =19
LDR r2, =20
STMDB SP, { r1, r2 }

[ERROR]

*** error 65: access violation at 0x00000000 : no 'write' permission

Here is the simplest code with startup after:

[MAIN] *(ALIGNS are placed there due to the alignment error, but make no difference if they are removed)

    GLOBAL user_code
AREA mycode, CODE, READONLY 

user_code
 LDR r1, =0x400000000
 ALIGN
 LDR r2, =19
 ALIGN
 STR r2, [r1]
 ALIGN
 END

[STARTUP]

; Standard definitions of Mode bits and Interrupt (I & F) flags in PSR s
Mode_USR EQU 0x10
I_Bit EQU 0x80 ; when I bit is set, IRQ is disabled
F_Bit EQU 0x40 ; when F bit is set, FIQ is disabled
;Defintions of User Mode Stack and Size
USR_Stack_Size EQU 0x00000100
;USR_Stack_Size EQU 0x7FFF
SRAM EQU 0x40000000
Stack_Top EQU SRAM+USR_Stack_Size

    AREA RESET, CODE, Readonly
    ENTRY ; The first instruction to execute follows
    ARM
    IMPORT user_code
VECTORS
    LDR PC, Reset_Addr
    LDR PC, Undef_Addr
    LDR PC, SWI_Addr
    LDR PC, PAbt_Addr
    LDR PC, DAbt_Addr
    NOP
    LDR PC, IRQ_Addr
    LDR PC, FIQ_Addr
Reset_Addr DCD user_code
Undef_Addr DCD UndefHandler
SWI_Addr DCD SWIHandler
PAbt_Addr DCD PAbtHandler
DAbt_Addr DCD DAbtHandler
    DCD 0
IRQ_Addr DCD IRQHandler
FIQ_Addr DCD FIQHandler
SWIHandler B SWIHandler
PAbtHandler B PAbtHandler
DAbtHandler B DAbtHandler
IRQHandler B IRQHandler
FIQHandler B FIQHandler
UndefHandler B UndefHandler
    ; Enter User Mode with interrupts enabled
MOV r14, #Mode_USR
BIC r14,r14,#(I_Bit+F_Bit)
MSR cpsr_c, r14
;initialize the stack, full descending
LDR SP, =Stack_Top
;load start address of user code into PC
LDR PC, =user_code
;IMPORT Reset_Handler
END

[ERROR]

Non-aligned Access: ARM Instruction at 00000080H, Memory Access at 00000013H
*** error 65: access violation at 0x00000013 : no 'write' permission

dont put aligns between instructions anyway, because that potentially will add extra data in your instruction stream which is bad. the instructions are aligned anyway which is what you already figured out.

your code needs to do something after the str otherwise it just wanders into (executes int) garbage or whatever is after that code which may eventually run off the end and hit a prefetch abort...If your tools allow for this then put:

b .

otherwise

label: b label