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CHAPTER 3 CP0 REGISTERS
User’s Manual U14272EJ3V0UM
76
3.2.10 Compare register (11)
The Compare register causes a timer interrupt; it maintains a stable value that does not change on its own.
When the value of the Count register (see
3.2.8 Count register (9)
) equals the value of the Compare register, the
IP7 bit in the Cause register is set. This causes an interrupt as soon as the interrupt is enabled. Writing a value to
the Compare register, as a side effect, clears the timer interrupt request.
For diagnostic purposes, the Compare register is a read/write register. Normally, this register should be only used
for a write.
The contents of the Compare register are undefined after a reset.
Figure 3-11. Compare Register
0
31
Compare
Compare: Value that is compared with the count value of the Count register.
3.2.11 Status register (12)
The Status register is a read/write register that contains the operating mode, interrupt enabling, and the diagnostic
states of the processor.
Figure 3-12. Status Register (1/2)
29 28 27 26 25 24
16 15
8
7
6
5
3
2
1
0
31
0
CU0
0
RE
DS
IM
UX
KSU
ERL
IE
KX SX
EXL
4
CU0:
Enables/disables the use of the coprocessor (1
→
Enabled, 0
→
Disabled).
CP0 can be used in Kernel mode at all times.
Enables/disables reversing of the endian setting in User mode (0
→
Disabled, 1
→
Enabled). This
bit must be set to 0 since the V
R
4181 supports the little-endian order only.
Diagnostic Status field (see
Figure 3-13
).
Interrupt mask field used to enable/disable interrupts (0
→
Disabled, 1
→
Enabled). This field
consists of 8 bits that are used to control eight interrupts. The bits are assigned to interrupts as
follows:
IM7:
Masks a timer interrupt.
IM(6:2):
Mask ordinary interrupts (Int(4:0)
IM(1:0):
Mask software interrupts.
RE:
DS:
IM:
Note
). However, Int(4:3)
Note
never occur in the V
R
4181.
Note
Int(4:0) are internal signals of the V
R
4110 CPU core. For details about connection to
the on-chip peripheral units, refer to
CHAPTER 9 INTERRUPT CONTROL UNIT
(ICU)
.