Internal PWRGOOD
Note: If VTR is to be used for programmable
wake-up events when VCC is removed, VTR must
be at its full minimum potential at least 10 μs
before Vcc begins a power-on cycle. When VTR
and Vcc are fully powered, the potential difference
between the two supplies must not exceed
500mV.
An internal PWRGOOD logical control is included
to minimize the effects of pin-state uncertainty in
the host interface as Vcc cycles on and off.
When the internal PWRGOOD signal is “1”
(active), Vcc is > 4V, and the FDC37B78x host
interface is active.
When the internal
PWRGOOD signal is “0” (inactive), Vcc is ≤ 4V,
and the FDC37B78x host interface is inactive;
that is, ISA bus reads and writes will not be
decoded.
CIRCC PLL Power Control
The FDC37B78x uses the 32.768 kHz RTC clock
and a clock multiplier (PLL) to drive the CIrCC
Wakeup function when Vcc has been removed.
The CIR PLL Power bit, located in the
Sleep/Wake Configuration Register, is used to
enable (power-up) the 32.768 kHz clock PLL.
When the CIR PLL Power bit is set to “1”
(active), the 32.768 kHz clock PLL is running and
can replace the 14.318 MHz clock source for the
CIR Wake Event, depending upon the state of
the internal PWRGOOD signal (TABLE 51).
When the CIR PLL Power bit is reset to “0”
(inactive/default), the 32.768 kHz clock PLL is
unpowered.
The FDC37B78x device pins nPME, KCLK,
MCLK, IRRX, nRI1, nRI2, RXD1, RXD2, nRING,
Button_In and GP53 are part of the PME
interface and remain active when the internal
PWRGOOD signal has gone inactive, provided
VTR is powered. In addition, the nPowerOn and
CLK32OUT pins remain active when the internal
PWRGOOD is inactive and VTR is powered.
When the internal PWRGOOD is inactive, and
VTR is powered, the GPIOs (excluding GP53)
become tri-state (input) and are able to generate
wake-up events. The internal PWRGOOD signal
is also used to determine the clock source for the
CIrCC CIR and to disable the IR Half Duplex
Timeout.
TABLE 51 - FDC37B78x PLL CONTROLS AND SELECTS
PLL CONTROL
BIT (CR24.1)
CIR PLL
POWER BIT
INTERNAL
PWRGOOD
DESCRIPTION
All PLLs Powered Down
1
0
0
X
0
0
X
0
1
32KHz PLL Unpowered, Not Selected,
14MHz PLL Powered, Selected.
32KHz PLL Powered, Selected,
14MHz PLL Unpowered, Not Selected.
32KHz PLL Powered, Not Selected, 14MHz PLL
Powered, Selected.
0
0
1
1
0
1
32.768 kHz Standby Clock Output
The FDC37B78x provides a 32.768 kHz trickle clock output pin. This output is active as long as VTR is
present.
SERIAL INTERRUPTS
The FDC37B78x will support the serial interrupt to transmit interrupt information to the host system. The
serial interrupt scheme adheres to the Serial IRQ Specification for PCI Systems, Version 6.0.
116
SMSC [ SMSC CORPORATION ]
