PDI1394L41 Datasheet, PDF (15/81 Pages) NXP Semiconductors – 1394 content protection AV link layer controller

Philips Semiconductors
1394 content protection AV link layer controller
Preliminary specification
PDI1394L41
12.3 Bushold and Link/PHY single capacitor galvanic isolation
12.3.1 Bushold
The PDI1394L41 uses an internal bushold circuit on each of the indicated pins to keep these CMOS inputs from “floating” while being driven by
a 3-Stated device or input coupling capacitor. Unterminated high impedance inputs react to ambient electrical noise which cause internal
oscillation and excess power supply current draw.
The following pins have bushold circuitry enabled when the ISON pin is in the logic “1” state:
Name
PHY CTL0
PHY CTL1
PHY D0
PHY D1
PHY D2
PHY D3
PHY D4
PHY D5
PHY D6
PHY D7
Function
PHY control line 0
PHY control line 1
PHY data bus bit 0
PHY data bus bit 1
PHY data bus bit 2
PHY data bus bit 3
PHY data bus bit 4
PHY data bus bit 5
PHY data bus bit 6
PHY data bus bit 7
Philips bushold circuitry is designed to provide a high resistance pull-up or pull-down on the input pin. This high resistance is easily overcome
by the driving device when its state is switched. Figure 2 shows a typical bushold circuit applied to a CMOS input stage. Two weak MOS
transistors are connected to the input. An inverter is also connected to the input pin and supplies gate drive to both transistors. When the input
is LOW, the inverter output drives the lower MOS transistor and turns it on. This re-enforces the LOW on the input pin. If the logic device which
normally drives the input pin were to be 3-Stated, the input pin would remain “pulled-down” by the weak MOS transistor. If the driving logic
device drives the input pin HIGH, the inverter will turn the upper MOS transistor on, re-enforcing the HIGH on the input pin. If the driving logic
device is then 3-Stated, the upper MOS transistor will weakly hold the input pin HIGH.
The PHY’s outputs can be 3-Stated and single capacitor isolation can be used with the Link; both situations will allow the Link inputs to float.
With bushold circuitry enabled, these pins are provided with dc paths to ground, and power by means of the bushold transistors; this
arrangement keeps the inputs in known logical states.
INPUT PIN
INTERNAL
CIRCUITS
Figure 2. Bushold circuit
SV00911
2000 Apr 15
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