Functional Description
3–17
Reset and Initialization
At system reset, the 21164 microprocessor’s procirq<3:0> pins are driven by the
clock divisor values set by four jumpers on J28. During normal operation, these sig-
nals are used for interrupt requests. The pins are either switched to ground or pulled
up in a specific combination to set the 21164 microprocessor’s internal divider.
The 21164 microprocessor produces the divided clock output signal sysclk that
drives the CY2308 PLL clock-driver chip. This clock provides the references to syn-
chronize the 21164 microprocessor and the 21174 chip. The 21174 provides the sys-
tem memory and I/O (PCI) clock references. It also provides system-level clocking
to DIMMs, PCI 64slot, the PCI-ISA bridge, the PCI-PCI controller,Ethernet Control-
ler, DMA Hack and the PCI arbiter.
3.7 Reset and Initialization
An external reset switch can be connected to J37 (pc164UX.35). The reset function
initializes the 21164 microprocessor and the system logic. The vccok signal provides
a full system initialization, equivalent to a power-down and power-up cycle.
When dc_ok signal is inserted to 21174 chip, 21174 chip drives *p64_rst signal to
reset primary PCI devices and PCI to PCI bridge.
As soon as *p64_rst is inserted, PCI to PCI bridge drives *p32_rst signal to reset
secondary PCI devices
Figure 3–7 System Reset and Initialization
Power Supply
Reset Switch
vccok
pc164ux.34
pc164ux.35
J18
J37
8
2
1
21164
pc164ux.2
dc_oka
*dc_ok
dc_ok
*rstswitch
pc164ux.35
HC125D
HCT14D
pc164ux.35
21174
pc164ux.10
*p64_rst
pci 64 slot
pci - isa bridge
ethernet controller
dma hack
pci-pci
pc164ux.19
*p32_rst
SCSI controller
pci 32 slots
*cpureset
