CY7C67300
Document #: 38-08015 Rev. *J
Page 16 of 99
Registers
Some registers have different functions for a read vs. a write
access or USB host vs. USB device mode. Therefore, registers
of this type have multiple definitions for the same address.
The default register values listed in this data sheet may be
altered to some other value during the BIOS initialization. Refer
to the BIOS documentation for register initialization information.
Processor Control Registers
There are nine registers dedicated to general processor control.
Each of these registers are covered in this section and are
summarized in
Table 21
.
CPU Flags Register [0xC000] [R]
Register Description
The CPU Flags register is a read only register that gives
processor flags status.
Global Interrupt Enable
(Bit 4)
The Global Interrupt Enable bit indicates if the Global Interrupts
are enabled.
1:
Enabled
0:
Disabled
Negative Flag
(Bit 3)
The Negative Flag bit indicates if an arithmetic operation results
in a negative answer.
1:
MS result bit is ‘1’
0:
MS result bit is not ‘1’
Overflow Flag
(Bit 2)
The Overflow Flag bit indicates if an overflow condition occurred.
An overflow condition can occur if an arithmetic result was either
larger than the destination operand size (for addition) or smaller
than the destination operand must allow for subtraction.
1:
Overflow occurred
0:
Overflow did not occur
Carry Flag
(Bit 1)
The Carry Flag bit indicates if an arithmetic operation resulted in
a Carry for addition, or Borrow for subtraction.
1:
Carry/Borrow occurred
0:
Carry/Borrow did not occur
Zero
Flag (Bit 0)
The Zero Flag bit indicates if an instruction execution resulted in
a ‘0’.
1:
Zero occurred
0:
Zero did not occur
Table 21. Processor Control Registers
Register Name
Address
R/W
CPU Flags Register
0xC000
R
Register Bank Register
0xC002
R/W
Hardware Revision Register
0xC004
R
CPU Speed Register
0xC008
R/W
Power Control Register
0xC00A
R/W
Interrupt Enable Register
0xC00E
R/W
Breakpoint Register
0xC014
R/W
USB Diagnostic Register
0xC03C
W
Memory Diagnostic Register
0xC03E
W
Table 22. CPU Flags Register
Bit #
15
14
13
12
11
10
9
8
Field
Reserved...
Read/Write
-
-
-
-
-
-
-
-
Default
0
0
0
0
0
0
0
0
Bit #
7
6
5
4
3
2
1
0
Field
...Reserved
Global
Interrupt
Enable
Negative
Flag
Overflow
Flag
Carry
Flag
Zero
Flag
Read/Write
-
-
-
R
R
R
R
R
Default
0
0
0
X
X
X
X
X
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