The Cortex-M4 processor
PM0214
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PM0214 Rev 10
These registers are mutually exclusive bitfields in the 32-bit PSR. The bit assignment is 
shown in Figure 3 and Figure 4.
Figure 3. APSR, IPSR and EPSR bit assignment
Figure 4. PSR bit assignment 
Access these registers individually or as a combination of any two or all three registers, 
using the register name as an argument to the MSR or MRS instructions. For example:
•
Read all of the registers using PSR with the MRS instruction.
•
Write to the APSR N, Z, C, V, and Q bits using APSR_nzcvq with the MSR instruction.
The PSR combinations and attributes are:
          
See the instruction descriptions MRS on page 186 and MSR on page 187 for more 
information about how to access the program status registers.
Table 4. PSR register combinations 
Register
Type
Combination
PSR
read-write(1), (2)
1.
The processor ignores writes to the IPSR bits.
2.
Reads of the EPSR bits return zero, and the processor ignores writes to the these bits
APSR, EPSR, and IPSR
IEPSR
read-only
EPSR and IPSR
IAPSR
read-write(1)
APSR and IPSR
EAPSR
read-write(2)
APSR and EPSR
25 24 23
Reserved
ISR_NUMBER
31 30 29 28 27
N Z C V
0
Reserved
APSR
IPSR
EPSR
Reserved
Reserved
26
16 15
10 9
Reserved
ICI/IT
ICI/IT
T
Q
8
19
20
GE[3:0]
Reserved
25 24 23
31 30 29 28 27
N Z C V
0
PSR
Reserved
26
16 15
10 9
ICI/IT
Q
8
19
20
GE[3:0]
Reserved
ISR_NUMBER
