Nintendo GAME BOY Programming Manual page 123

CCF
Flips the carry flag CY.
Example: When CY = 1,
; CY ← 0
CCF
SCF
Sets the carry flag CY.
DI
Resets the interrupt master enable flag and prohibits maskable interrupts.
Note: Even if a DI instruction is executed in an interrupt routine, the IME flag is
set if a return is performed with a RETI instruction.
EI
Sets the interrupt master enable flag and enables maskable interrupts.
This instruction can be used in an interrupt routine to enable higher-order interrupts.
Note: The IME flag is reset immediately after an interrupt occurs. The IME flag
reset remains in effect if control is returned from the interrupt routine by
a RET instruction. However, if an EI instruction is executed in the
interrupt routine, control is returned with IME = 1.
CY ← (CY)
CY ← 1
IME ← 0
IME ← 1
123
Chapter 4: CPU Instruction Set
CY H N Z CYCL
0 0 -- 1
(CY)
CY H N Z CYCL
1 0 0 -- 1
CY H N Z CYCL
-- -- -- -- 1
CY H N Z CYCL
-- -- -- -- 1
7 6 5 4 3 2 1 0
00 111 111
7 6 5 4 3 2 1 0
00 110 111
7 6 5 4 3 2 1 0
11 110 011
7 6 5 4 3 2 1 0
11 111 011