SBPH400-3 Ver la hoja de datos (PDF) - STMicroelectronics
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SBPH400-3 Datasheet PDF : 43 Pages
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SBPH400-3
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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