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PEB 3445 E
Functional Description
Data Sheet
57
2001-06-29
Link). If the transmit command does not include a ’Transmit Message End’ indication
(FHND.XME, PHND.XME), the signalling controller will repeatedly request for the next
data block by means of a XPR interrupt as soon as the transmit FIFO becomes free. This
process will be repeated until the local CPU writes the last bytes to the transmit FIFO.
End of transmission is by issuing the command ’Stop Transmission’. In case of C-bit
Parity Path Maintenance Data Link channel CRC and closing flag sequence is appended
after the last byte was sent.
C-bit parity path maintenance data link channel only: Consecutive frames may share a
flag (enabled via bit PXCR.SF) or may be transmitted as back-to-back frames, if service
of transmit FIFO is quick enough. In case that no more data is available in the transmit
FIFO prior to the arrival of PHND.XME, the transmission of the frame is terminated with
an abort sequence and the CPU is notified via a ’Transmit Data Underrun’ interrupt
(XDU). The frame may also be aborted per software by setting the XAB bit in the
handshake register PHND.
In case of messages longer than 32 bytes the transmit FIFO has to be filled up in blocks
of 32 bytes. The last block of the message can be smaller than 32 bytes. If the transmit
FIFO is not filled up in time a transmit abort (C-bit parity Path Maintenance Data Link) is
inserted or gaps between BOM messages (Far End Alarm and Control Channel) may
occur.
Figure 11
Interrupt Driven Transmit Sequence Example
Note: Data bus is 16 bit wide. In the given example writing 32 bytes requires 16 write
accesses. Writing 15 bytes requires 8 accesses.
WR
15 bytes
WR
32 bytes
XTF
32 bytes
32 bytes
15 bytes
XTF
Transmit frame (79 bytes)
FDL channel
Local Bus
Interface
WR
32 bytes
XTF+XME
XPR
XPR
XPR
ALLS