Datasheet

Programmer’s Model
ARM7TDMI Data Sheet
ARM DDI 0029E
3-9
Open Access
Interrupt disable bits The I and F bits are the interrupt disable bits. When set,
these disable the IRQ and FIQ interrupts respectively.
The mode bits The M4, M3, M2, M1 and M0 bits (M[4:0]) are the mode
bits. These determine the processor’s operating mode,
as shown in ➲ Table 3-1: PSR mode bit values on page
3-9. Not all combinations of the mode bits define a valid
processor mode. Only those explicitly described shall be
used. The user should be aware that if any illegal value
is programmed into the mode bits, M[4:0], then the
processor will enter an unrecoverable state. If this
occurs, reset should be applied.
Reserved bits The remaining bits in the PSRs are reserved. When
changing a PSR’s flag or control bits, you must ensure
that these unused bits are not altered. Also, your
program should not rely on them containing specific
values, since in future processors they may read as one
or zero.
M[4:0] Mode Visible THUMB state
registers
Visible ARM state
registers
10000 User R7..R0,
LR, SP
PC, CPSR
R14..R0,
PC, CPSR
10001 FIQ R7..R0,
LR_fiq, SP_fiq
PC, CPSR, SPSR_fiq
R7..R0,
R14_fiq..R8_fiq,
PC, CPSR, SPSR_fiq
10010 IRQ R7..R0,
LR_irq, SP_irq
PC, CPSR, SPSR_irq
R12..R0,
R14_irq..R13_irq,
PC, CPSR, SPSR_irq
10011 Supervisor R7..R0,
LR_svc, SP_svc,
PC, CPSR, SPSR_svc
R12..R0,
R14_svc..R13_svc,
PC, CPSR, SPSR_svc
10111 Abort R7..R0,
LR_abt, SP_abt,
PC, CPSR, SPSR_abt
R12..R0,
R14_abt..R13_abt,
PC, CPSR, SPSR_abt
11011 Undefined R7..R0
LR_und, SP_und,
PC, CPSR, SPSR_und
R12..R0,
R14_und..R13_und,
PC, CPSR
11111 System R7..R0,
LR, SP
PC, CPSR
R14..R0,
PC, CPSR
Table 3-1: PSR mode bit values