S3C44B0X データシートの表示（PDF） - Samsung

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S3C44B0X

RISC MICROPROCESSOR

Samsung 

S3C44B0X RISC MICROPROCESSOR

PROGRAMMER'S MODEL

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PROGRAMMER'S MODEL

OVERVIEW

S3C44B0X has been developed using the advanced ARM7TDMI core, which has been designed by Advanced

RISC Machines, Ltd.

PROCESSOR OPERATING STATES

From the programmer's point of view, the ARM7TDMI can be in one of two states:

• ARM state which executes 32-bit, word-aligned ARM instructions.

• THUMB state which can execute 16-bit, halfword-aligned THUMB instructions. In this state, the PC uses bit 1

to select between alternate halfwords.

NOTE

Transition between these two states does not affect the processor mode or the contents of the registers.

SWITCHING STATE

Entering THUMB State

Entry into THUMB state can be achieved by executing a BX instruction with the state bit (bit 0) set in the operand

register.

Transition to THUMB state will also occur automatically on return from an exception (IRQ, FIQ, UNDEF, ABORT,

SWI etc.), if the exception was entered with the processor in THUMB state.

Entering ARM State

Entry into ARM state happens:

• On execution of the BX instruction with the state bit clear in the operand register.

• On the processor taking an exception (IRQ, FIQ, RESET, UNDEF, ABORT, SWI etc.). In this case, the PC is

placed in the exception mode's link register, and execution commences at the exception's vector address.

MEMORY FORMATS

ARM7TDMI views memory as a linear collection of bytes numbered upwards from zero. Bytes 0 to 3 hold the first

stored word, bytes 4 to 7 the second and so on. ARM7TDMI can treat words in memory as being stored either in

Big-Endian or Little-Endian format.

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