TSB12C01A datasheet(20/38 Pages) TI

20 / 38 page

TSB21LV03

IEEE 1394-1995 TRIPLE-CABLE TRANSCEIVER/ARBITER

SLLS230A – MARCH 1996 – REVISED DECEMBER 1996

POST OFFICE BOX 655303

• DALLAS, TEXAS 75265

APPLICATION INFORMATION

The capacitive-isolation circuit and the transformer-isolation circuit operate basically the same. In order for

signals to cross the isolation boundary, the driving side output must first be differentiated. Whenever the line

state changes, the phy-LLC interface signal is driven to the new state. When the line state remains constant

for more than one clock period, the signal is sent into a high-impedance state. When the output signal is at the

high-impedance state, the input signals quickly return to VDD/2. The differentiation is handled internally in the

phy and LLC integrated circuits. Figure 10 shows the logical line state at the output buffer, VL, when the LLC

is driving, and VP when the phy is driving.

ZZZ

Undifferentiated Phy/LLC

Interface Signal

Differentiated Phy/LLC

Interface Output Signal

Figure 10. Differentiation of Interface Signal (ISO Terminal low)

The signal at the input buffer is shown in the Figure 11. This waveform is for a 5-V device. A 3-V device would

have the signals ratioed down accordingly.

2.5

VIT+

VIT–

Schmitt Trigger Input

Buffer Thresholds

Figure 11. Line Levels of Differentiated Interface Signals

The input buffer output remains in its previous state until a hysteresis threshold is crossed, thus recreating the

original undifferentiated signal. To turn the ISO terminal on for Texas Instruments devices, it must be held to

a low logic level.

TSB12C01A Datasheet(PDF) 20 Page - Texas Instruments