SBPH400-3 datasheet(32/43 Pages) STMICROELECTRONICS

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SBPH400-3

2.9.4 LKON (link on)

The LKON pin is used as an output to indicate that the SBPH400 has received a Link_On

packet. If the there is no signal on the LPS pin (indicating that the link device is not currently

powered) or the Link_active register is zero (link interface turned off by software) and a

Link_On packet is received addressed to the node, then a 6.144 MHz signal is output on the

LKON pin. This signal is turned off within 500 ns when both there is a signal received on LPS

and the Link_active register is 1.

2.10 ISO (isolation)

The SBPH400 supports the use of an isolation barrier between the chip and a link device. If

ISO is set high, then the an internal pulsed differentiating function is used on the CTL[0:1] and

the D[0:7] pins when used as outputs. Appropriate threshold circuitry is included on these pins

when used as inputs to interpret differentiated signals correctly. The differentiation circuitry

transmits a 1 or a 0 when there is a logical transition to 1 or 0 respectively, otherwise the output

is set to high impedance. This is shown in Table 2.22. This allows an arbitrary sequence of 1’s

or 0’s to be transmitted across an AC coupled isolation interface.

2.11 CPS (cable power status)

This input should be connected to the power supply provided from the cable via an external

series 400 KOhm resistor. The internal logic associated with this pin provides a nominal filtered

cable power fail voltage (as applied to the external resistor) threshold of 6.25 volts. The internal

logic will report 1 in the PS register when the external voltage on the resistor exceeds the

threshold, and will report 0 in the PS register when the external voltage falls below the

threshold. A transition from 1 to 0 on the value in the PS register causes the Pwr_fail register

to be set to 1, which in turn will cause a link status transfer with the PHY_Interrupt bit set if the

Link interface is active, otherwise will cause a LinkOn signal. Appropriate protection is

incorporated in the SBPH400 for cable power voltages within the 1394 specification applied

via the external series resistor.

Table 2.22

Output differentiation for isolation

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