CN8478 Datasheet, PDF (158/221 Pages) Conexant Systems, Inc – Multichannel Synchronous Communications Controller (MUSYCC)

6.0 Basic Operation
6.3 Channel Operation
CN8478/CN8474A/CN8472A/CN8471A
Multichannel Synchronous Communications Controller (MUSYCC™)
6.3.18 Channel Jump
A channel jump request is issued by the host via a service request. For a receiver,
channel jumps are the same as channel activation.
For a transmitter, channel jumps are non-destructive to currently serviced
messages. The channel state is not reset as in the channel activate sequence.
Therefore, a transmitter channel must be activated first, then subsequent jump
requests can be made using the channel jump service request. For a transmitter,
channel jumps provide a non-destructive way to start transmitting a new message
list. MUSYCC waits until the completion of the current message before jumping
to a message list pointed to by a new Head Pointer.
A jump request is issued by the host via a service request towards a channel in
a channel group in MUSYCC.
NOTE: The service request acknowledge (via the SACK Interrupt Descriptor) for
the jump service request—specifically for the transmit direction—will not
be output towards the host until after the current message is transmitted.
For applications with long messages to transmit, the jump service request
must be used with care.
6.3.19 Frame Alignment
Each serial port frame consists of a fixed number of bits grouped into time
slots according to the frame alignment supplied by the serial port TSYNC and
RSYNC signals. MUSYCC must be provided at least one external
synchronization pulse on the TSYNC and RSYNC input pins after the respective
channel group is enabled. After this initial sync pulse, MUSYCC tracks
subsequent serial port frame boundaries using its internal flywheel mechanism or
the next applied sync pulse.
NOTE: Nx64 serial port mode does not operate the internal flywheel and therefore
requires periodic TSYNC and RSYNC pulses to keep track of serial port
frame boundaries.
In addition to tracking serial port frame boundaries, the internal flywheel
generates a frame synchronization signal that can be selected to control the
channel group's alignment of Transparent mode channel data streams. By default,
the frame synchronization signal from the internal flywheel determines
Transparent mode channel data stream alignment. If external data stream
synchronization is preferred, the SFALIGN bit field in the Group Configuration
Descriptor can be set to expect this synchronization signal to come from the serial
port TSYNC and RSYNC input pins. While SFALIGN is set, the internal
flywheel continues to operate, but the synchronization signal from the flywheel is
not used to determine data stream alignment. Instead, alignment is provided by
the external framer device which is allowed to strobe the sync input pins at
periodic frame intervals or at any desired multiple of the frame interval
(i.e., superframe).
Each serial port frame carries stream data from one or more packetized HDLC
or unpacketized Transparent mode channels. Although channels are mapped to
specific time slots within the serial port frame, each channel's data streaming
process may or may not have a particular alignment with respect to that channel's
assigned time slot boundaries, depending upon whether the channel is configured
to operate in HDLC or Transparent mode.
6-24
Conexant
100660E