PC87373 datasheet(32/174 Pages) NSC

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2.0 Power, Reset and Clocks (Continued)

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Figure 3. 32 KHz and 48 MHz Clock Domains (Simpliﬁed Diagram)

2.3.3

32 KHz Domain

The 32 KHz clock domain, and the modules using it, are supplied by the Standby and Core power planes. Therefore, this

clock domain is active whenever the VSB3 and VCORF power supplies are on.

The 32 KHz clock domain is sourced by the CLOCKI32 pin. The clock signal from the CLOCKI32 pin passes through a Clock

Filter. The 32 KHz clock domain signal is held low by the 32KVAL output of the Clock Filter until a valid 32.768 KHz clock is

available at the CLOCKI32 pin. The 32 KHz clock domain signal starts toggling t32KW +t32KVAL after VSB3 Power-Up (Low-

Frequency Clock Timing on page 162).

2.4 TESTABILITY SUPPORT

The PC87373 device supports two testing techniques:

• In-Circuit Testing (ICT)

• XOR Tree Testing

2.4.1

ICT

The In-Circuit Testing (ICT) technique, also known as “bed-of-nails”, injects logic patterns to the input pins of the devices

mounted on the tested board. It then checks their outputs for the correct logic levels.

The PC87373 supports this testing technique by floating (TRI-STATing) all the device pins. This prevents “back-driving” the

PC87373 pins by the ICT tester when a device normally controlled by PC87373 is tested (device inputs are driven by the

ICT tester).

To enter TRI-STATE mode, the TRIS pin must be pulled low (by a 10 K

Ω resistor to V

SS), and the TEST pin must be left

unconnected after both VDD3 and VSB3 power supplies are turned on. In addition, the PCI_RESET pin must be held low for

at least 10 ms (see VSB Power-Up Reset on page 159 and VDD Power-Up Reset on page 160). After PCI_RESET is de-

asserted, all the device output and I/O pins are floated (TRI-STATEd); exceptions to this are the power supply pins (VDD3,

VSB3, VSS, VCORF, VBAT), analog pins (VSB5, REF5V, REF5V_STBY), RSMRST, which do not float in TRI-STATE mode.

Clock

Generator

14.31818 MHz

CLOCKI14

Functions

Internal

48 MHz

CKVALID

(VDD3)

CLOCKI32

Functions

Internal

Filter

Clock

32.768 KHz

32KVAL

32 KHz Domain

48 MHz Domain

HFCGEN

PC87373 数据表(PDF) 32 Page - National Semiconductor (TI)

PC87373 数据表(HTML) 32 Page - National Semiconductor (TI)

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