cx28500 Mindspeed Technologies, cx28500 Datasheet - Page 76

• Manufacturer Part Number: cx28500
• Description: Cx28500 Multichannel Synchronous Communications Controller
• Manufacturer: Mindspeed Technologies

5.1
A receive serial port unit (RSIU) connects to four input signals: RCLK, RDAT, RSYNC, and ROOF. A transmit serial
port unit (TSIU) connects to three input signals and one output signal: TCLK, TSYNC, CTS, and TDAT, respectively.
The SIU is responsible for receiving and transmitting data bytes to the Transmit Serial Line Processor (TSLP) and
Receive Serial Line Processor (RSLP). The receive and transmit data and synchronization signals are
synchronous to the receive and transmit line clocks, respectively. CX28500 can be configured to sample in and
latch out data signals and sample in status and synchronization signals on either the rising or falling edges of the
respective line clock, namely RCLK and TCLK. This configuration is accomplished by setting the ROOF_EDGE,
RSYNC_EDGE, RDAT_EDGE, TSYNC_EDGE, and TDAT_EDGE bit fields as detailed in
Configuration Register
in and latch out data synchronization and status on the falling edges of the respective line clock. The port mode is
configured by programming the RPORT_TYPE and TPORT_TYPE bit fields in RSIU Port Configuration Register
and TSIU Port Configuration Register, respectively. When configured to operate in conventional mode, the
receive and transmit directions are not related to each other so that each direction can be programmed
independently of the other.
5.1.1
CX28500 utilizes the TSYNC and RSYNC signals to maintain a time-base, which 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
TSYNC or RSYNC input marks the first bit in the frame. The mode specified in the RPORT_TYPE bit field in
Table 6-28, RSIU Port Configuration Register
Configuration Register
frame. A flywheel exists for both the transmit and the receive functions for every port.
The flywheel is synchronized when CX28500 detects TSYNC = 1 or RSYNC = 1, for transmit or receive functions,
respectively. Once synchronized, the flywheel maintains synchronization without further assertion of the
synchronization signal. Additional sync pulses do not interfere with the flywheel mechanism as long as they are
synchronized correctly.
A time slot counter within each port is reset once in each frame and tracks the current time slot being serviced. In
the receive side, synchronization starts at the beginning of frame. In the transmit side, however, synchronization
starts four time slots later since there is an associated latency between when the TSIU requests the TSLP for data
and when the TSLP supplies the TSIU with the requested data.
5.1.2
A Change Of Frame Alignment (COFA) condition is defined as a frame synchronization event detected when it was
not expected, and also includes the detection of the first occurrence of frame synchronization when none was
present. In unchannelized mode, there are no COFA conditions because the TSYNC and RSYNC signals are
ignored in this mode.
In the receive direction, when a COFA condition is detected by the serial interface, an internal COFA signal is
asserted until the COFA condition is declared off. A COFA condition is declared “off” when there was a complete
frame without an unexpected SYNC pulse. Thus, an internal COFA signal is asserted for at least two frame
periods. During the frame period that the internal COFA is asserted, CX28500’s serial line processor (SLP)
terminates all messages that are found to be active during the COFA condition. For each receiver and transmitter
channel found to be active and processing a message, the corresponding message descriptor’s owner bit is
28500-DSH-002-C
NOTE:
Serial Port Interface Definition in Conventional Mode
Frame Synchronization Flywheel
Change Of Frame Alignment (COFA)
and
and the start and end address of time slot pointer determines the number of bits in the
In unchannelized mode, CX28500 ignores the TSYNC and RSYNC signals and the frame
synchronization flywheel mechanism is ignored.
Table 6-36, TSIU Port Configuration
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and TPORT_TYPE bit field in
®
Register. The default, after reset, is to sample
Table 6-36, TSIU Port
Table 6-28, RSIU Port
Serial Interface
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