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4. Reset
This chapter discusses the reset types and reset sources on the ZT 5504. If necessary, the
ZT 5504's board reset characteristics can be tailored to the requirements of a specific system.
Reset Types and Sources
The ZT 5504's reset types are listed below. The sources for each reset type are detailed in the
following topics.
•
Hard Reset:
All devices are held in reset.
•
Soft Reset:
CPU initialization only. Other devices are not reset.
•
Backend Power Down:
The backend logic is powered off. The board is powered on and is
held in reset.
•
NMI:
Non-maskable interrupt. Though not a reset in the strict sense, an NMI can have the
same effect as other resets.
Hard Reset Sources
Faceplate Reset Push-button (SW-1)
Press push-button SW-1 on the ZT 5504's faceplate to issue a system reset.
System Register CF9h (PIIX4E Reset Control Register)
Bits 1 and 2 in this register are used by the PIIX4E to generate a hard reset or a soft reset.
During a hard reset, the PIIX4E asserts CPURST, PCIRST#, and RSTDRV, and resets its core
and suspend well logic.
Soft Reset Sources
System Register CF9h (PIIX4E Reset Control Register)
Bits 1 and 2 in this register are used by the PIIX4E to generate a hard reset or a soft reset.
During a soft reset, the PIIX4E asserts INIT to the CPU. This causes the processor to enter
"real mode", initialize its internal registers, and begin instruction execution from FFFFFFF0h
(the boot vector).
Keyboard Controller Reset
The keyboard controller generates a keyboard controller reset when FEh is written to port 64h.
This causes the PIIX4E to assert INIT to the CPU.
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