SBPH400-3 datasheet(9/43 Pages) STMICROELECTRONICS

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SBPH400-3

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2.4

Suspend/Resume/Disable

Each port independently implements the P1394a suspend/resume proposal. At any one time,

a port may be disconnected, disabled, suspended or active.

On power reset, if PDISABLE = 0 then all ports are initialized as disconnected, and then, if any

ports are physically connected, the normal new connection actions taken. If PDISABLE = 1

then all ports are initialized as disabled.

When a port is not active, the TpBias output for the port is disabled, all outputs of the port are

set to high impedance and any incoming arbitration signals on TPA and TPB are ignored.

A port may be disabled or re-enabled by a command (register write) from the local link, or by

remote PHY command packet. While disabled, the port ignores any incoming TpBias signal

but the port continues to monitor its connection status using the connect_detect mechanism.

A change in connection status will cause an interrupt to the link or a LinkOn packet as

appropriate and according to the controlling flags. When re-enabled and connected, the port

is treated as suspended (see below).

When disconnected, a port ignores any incoming TpBias signal but continuously monitors the

connection status using the connect detect circuitry. On connection, the port attempts to

become active, but if an incoming TpBias is not then detected, then the port is suspended with

the fault bit set.

While active, the port continuously senses the common-mode bias input voltage on the TPB

pair. The presence of a bias voltage on the TPB pair indicates that the port is connected to an

active port on some other device. Similarly, the absence of a bias voltage indicates the lack of

such a connection or that the far end port has been powered off. On detection of loss of bias,

the port is treated as suspended (see below)

A port may be suspended by a remote PHY command packet. In this case, it engages in a

protocol with the remote connected port, resulting in that port too being suspended. It may be

suspended on loss of incoming TpBias on an active port. A port may also be suspended as a

result of its active connected port being suspended. A connected disabled port is treated as

suspended when re-enabled.

While suspended, the port monitors both TpBias and its connection state using the

connect_detect mechanism. If a disconnection is detected, then the port becomes

disconnected. If a TpBias signal is detected, then the port resumes to its active state. A port

may be instructed to resume by means of a remote command packet, in which case it

generates a TpBias signal. This will indicate to the connected peer port that it too should

resume.

It should be noted that any change of port state to or from the active state has the effect of a

topology change, and that reconfiguration of the bus is necessary. To ensure that this occurs,

the SBPH400 initiates the appropriate bus resets as defined in the P1394a proposal.

When a port becomes disconnected, disabled or suspended, it carries out the appropriate

actions and then automatically enters a low power mode. Normal operation (on full power) is

restored after an appropriate delay (to allow the internal clocks to stabilize) on any change in

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