PEB 3445 E
Functional Description
Data Sheet
55
2001-06-29
Maintenance data link channel are named PRFF and PXFF respectively. The FIFOs of
the Far End Alarm and Control Channel are named FRFF and FXFF. FIFO status and
commands are exchanged using the port status registers PPSR (FPSR) and the
handshake register PHND (FHND). The C-bit parity Path Maintenance Data Link
Channel supports an external DMA controller via the signals DRR, RME or DRT and
TXME. Additional interrupts inform the system software about protocol status and FIFO
status.
4.6.3.1
Interrupt Driven Microprocessor Operation
Receive Direction
In receive direction there are different interrupt indications associated with the reception
of data:
A ’Receive Pool Full’ (RPF) interrupt indicates that a data block can be read from the
receive FIFO and the received message is not yet complete. It is generated, when the
amount of data bytes has reached the programmed threshold.
A ’Receive Message End’ (RME) or ’Receive Message Idle’ interrupt indicates that the
reception of one message is completed. After this interrupt system software has to
read the corresponding port status register in order to get the number of bytes stored
in the receive FIFO. This number includes the status byte which is written into the
receive FIFO as the last byte after the received frame. The status byte includes
information about the CRC result, valid frame indication, abort sequence or data
overflow. The format of the status byte is shown in the table below:
SMODE
STAT
Receiver Status Mode
Receive FIFO Status
This bit field reports the status of the data stored in the receive FIFO. The
content of the status byte is dependent on the channel.
7
6
5
4
0
SMODE(1:0)
0
STAT(4:0)
C-bit Parity Path
Maintenance Data Link
Valid HDLC Frame
Far End Alarm and
Control Channel
BOM Filtered data
declared
BOM Data Available
Flag 7E
H
Received
00000
B
00001
B
00010
B
Receive Data Overflow
Receive Abort