cx28560 Mindspeed Technologies, cx28560 Datasheet - Page 85

• Manufacturer Part Number: cx28560
• Description: Hdlc Controller
• Manufacturer: Mindspeed Technologies

CX28560 Data Sheet
4.7
4.7.1
4.7.2
28560-DSH-001-B
Serial Port Interface Definition TSBUS Mode
TSBUS Frame Synchronization Flywheel
TSBUS Group Synchronization Flywheel
A port operation mode is configured by programming the TPORT_TYPE and
RPORT_TYPE bit fields in RSIU and TSIU Port Configuration registers. When
configured to operate in TSBUS mode, the receive and transmit directions are
tied to each other. The same TPORT_TYPE/RPORT_TYPE must have the same
number of time slots configured for each TSBUS port, and TSTB must be
programmed the same for both directions, receive and transmit.
The CX28560 uses the TSTB signal to maintain a time-base that keeps track of
the active bit in the current time slot. The mechanism is referred to as the frame
synchronization flywheel. The flywheel counts the number of bits per frame and
automatically rolls over the bit count according to the programmed mode. The
TSTB input marks the first bit in the frame. A flywheel exists for both transmit
and the receive directions for each port. The TSTB assertion works the first bit of
time slot in the TSBUS frame. The flywheel is synchronized when the CX28560
detects TSTB = 1. Once synchronized, the flywheel maintains synchronization
without further assertion of the synchronization signal. A time slot counter within
each port is reset at the beginning of each frame and tracks the current time slot
being serviced.
In twelve of the CX28560’s serial ports, group extraction is supported. This mode
will normally be used to extract DS0 signals from a higher level of signal
multiplexing, though is fully configurable for any system. The group extraction
synchronization uses two extra signals, TGSYNC and RGSYNC, that are found
only in the first twelve ports in order to maintain a time-base that keeps track of
the active bit in the current time slot within a group. The mechanism is referred to
as the group synchronization flywheel.
The mechanism is used when the present time slot as pointed to in the frame
synchronization flywheel is configured to be a group time slot. In this case, the
group number is retrieved and the group time slot map is referred to. The
flywheel is synchronized when the CX28560 generates TGSYNC = 1 or detects
RGSYNC = 1. Once synchronized, the flywheel maintains synchronization
without further assertion of the group synchronization signal. The flywheel
counts the number of time slots per group and automatically rolls over the count.
The TGSYNC and the RGSYNC input marks the first time slot of a group.
Flywheels exist for both transmit and receive directions for each group.
Mindspeed Technologies™
Advance Information
CX28560 Serial Interface
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