Zilog Z80380 - Manual (Page 50)

5-16
Z380 ™
U SER ' S M ANUAL
DC-8297-03
Z ILOG
5.5.11 CPU Control Group
The instructions in this group (Table 5-16) act upon the
CPU control and status registers or perform other functions
that do not fit into any of the other instruction groups. These
include two instructions used for returning from an inter-
rupt service routine. Return from Nonmaskable Interrupt
(RETN) and Return from Interrupt (RETI) are used to pop
the Program Counter from the stack and manipulate the
Interrupt Enable Flag (IEF1 and IEF2), or to signal a reset
to the Z80 peripherals family.
The Disable and Enable Interrupt instructions are used to
set/reset interrupt mask. Without a mask parameters, it
disables/enables maskable interrupt globally. With mask
data, it enables/disables interrupts selectively.
HALT and SLEEP instructions stop the CPU and waits for
an event to happen, or puts the system into the power save
mode.
Bank Test instructions reports which register file, primary
or alternate bank, is in use at the time, and reflect the status
into a flag register. For example, this instruction is useful to
implement the recursive program, which uses the alter-
nate bank to save a register for the first time, and saves
registers into memory thereafter.
Mode Test instructions reports the current mode of opera-
tion, Native/Extended, Word/Long Word, Locked or not.
This instruction can be used to switch procedures de-
pending on the mode of operation.
Load Accumulator from R or I Register instructions are
used to report current interrupt mask status. Load from/to
register instructions are used to initialize the I register.
Load Control register instructions are used to read/write
the Status Register, set/reset control bit instructions and to
set/reset the control bits in the SR.
The No Operation instruction does nothing, and can be
used as a filler, for debugging purposes, or for timing
adjustment.
Table 5-16. CPU Control Group
Instruction Name Format
Bank Test BTEST
Disable Interrupt DI [mask]
Enable Interrupt EI [mask]
HALT HALT
Interrupt Mode Select IM p
Load Accumulator from I or R Register LD A,src
Load I or R Register from Accumulator LD dst,A
Load I Register from HL Register LD[W] HL,I
Load HL Register from I Register LD[W] HL,I
Load Control LDCTL dst,src
Mode Test MTEST
No Operation NOP
Return from Interrupt RETI
Return from Nonmaskable Interrupt RETN
Reset Control Bit RESC dst dst=LCK, LW
Set Control Bit SETC dst dst=LCK, LW, XM
Sleep SLP