SBPH400-3 datasheet(7/43 Pages) STMICROELECTRONICS

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SBPH400-3

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A port may be disconnected, disabled, suspended or active. When active, each port operates

in the following modes:

Idle mode: In this mode, each port’s driver is disabled, i.e. the port presents a high impedance

on all four signals. The inputs are continuously sampled, and if a signal is detected (which will

normally indicate an arbitration signal from a connected port) then this is passed to the

arbitration logic.

Arbitration mode: In this mode, both pairs engage in bi-directional untimed digital signalling.

Each pair transmits (under the control of the arbitration logic) either a logic 1 using differential

signalling, a logic 0 using differential signalling, or high impedance Z. Simultaneously, the

signal on each pair is continuously sampled, and is interpreted as a logic 1, logic 0 or high

impedance Z. The sampled signal is a combination of the transmitted signal and the signal

being transmitted on the corresponding pair by a connected transceiver (NB the cable

implements a “twist” - TPA is connected to the far end TPB, and vice versa). The signal is

interpreted using the 1394 1’s dominant rule and passed to the arbitration logic for

interpretation by the arbitration state machine. If a 11 level is received then this is interpreted

as a reset signal and passed to the control logic.

Speed signalling mode: Speed signalling uses common mode signalling. It is used to signal

the transmission speed capabilities of the device (during the Self_ID phase of bus initialization)

and in parallel with the transmission of Data_Prefix arbitration signal during arbitration to

indicate the speed of the packet about to be transmitted. To send a speed signal, the port

generates a common mode current signal on TPB and TPB# for 100 ns. This signal results in

a drop of the current mode bias voltage through a pair of 55 Ohm resistors connected between

the TpBias output and the TPA, TPA# pair at the receiving end. To receive a speed signal, the

port determines the speed by measuring the amount of voltage drop on the TPA pair,

compared to the TpBias signal it is generating. The port samples the speed signal at 20ns

intervals in order to provide filtering against intermediate values or against noise. The

SBPH400 requires two consecutive samples of a S200 or a S400 signal (as appropriate) in

order to identify a valid speed signal. If no speed signal is identified when data transmission

starts, then the data is assumed to be transmitted at S100 speed.

Data transmission mode: In this mode, which always follows arbitration mode, the port

transmits the data and strobe signals received from the data encoder on the TPB pair and the

TPA pair respectively. The transmission uses uni-directional differential data signalling on

each pair. Note that at the end of arbitration mode, the port will be transmitting an untimed

signal of 01. If the first bit to be transmitted is a zero, then this will cause a transition on “data”

(i.e. TPB, so that TPA, TPB transmit 00), if the first bit to be transmitted is a 1, then this will

cause a transition on “strobe” (i.e. TPA, so that TPA, TPB transmit 11). The receivers are

disabled during data transmission. At the end of data transmission mode, the port reverts to

idle mode.

Data reception mode: This mode always follows arbitration mode. The port presents high

impedance on its output drivers (and ignores the data which is being repeated to the other

ports by the data encoder/decoder). The port implements a differential receiver for each of

TPA (data) and TPB (strobe) pairs, and passes the received binary signals to the data

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