z80189 ZiLOG Semiconductor, z80189 Datasheet - Page 47

• Manufacturer Part Number: z80189
• Description: Z80180, Z8s180, Z8l180 Mpu Operation
• Manufacturer: ZiLOG Semiconductor

32
UM005003-0703
Z8018x
Family MPU User Manual
•
•
Essentially, the Z80180 operates normally in HALT mode, except that
instruction execution is stopped.
HALT mode can be exited in the following two ways:
•
•
If the interrupt source is masked (individually by enable bit, or globally
by IEF1 state), the Z80180 remains in HALT mode. However, NMI
interrupt initiates the normal NMI interrupt response sequence
independent of the state of IEF1.
HALT timing is illustrated in Figure 20.
The HALT output pin is asserted Low
The external bus activity consists of repeated dummy fetches of the
Op Code following the HALT instruction.
RESET Exit from HALT Mode
If the RESET input is asserted Low for at least six clock cycles,
HALT mode is exited and the normal RESET sequence (restart at
address
Interrupt Exit from HALT mode
When an internal or external interrupt is generated, HALT mode is
exited and the normal interrupt response sequence is initiated.
00000H
) is initiated.