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Data Sheet
685
Rev. 1.2, 2006-01-26
QuadFALC
TM
PEF 22554 E
Signaling Controller Operating Modes
12
Signaling Controller Operating Modes
The three HDLC controllers can be programmed to operate in various modes, which are different in the treatment
of the HDLC frame in receive direction. Thus, the receive data flow and the address recognition features can be
performed in a very flexible way, to satisfy almost any practical requirements.
There are 4 different operating modes which can be set via the mode registers (MODE, MODE2 and MODE3).
If not mentioned otherwise, all functions described for HDLC channel 1 apply to channel 2 and 3 as well.
12.1
HDLC Mode
All frames with valid addresses are forwarded directly via the RFIFO to the system memory.
Depending on the selected address mode, the QuadFALC
TM can perform a 1- or 2-byte address recognition
(MODE.MDS0).
If a 2-byte address field is selected, the high address byte is compared to the fixed value FEH or FCH (group
address) as well as with two individually programmable values in RAH1 and RAH2 registers. According to the
ISDN LAPD protocol, bit 1 of the high byte address is interpreted as command/response bit (C/R) and is excluded
from the address comparison.
Similarly, two compare values can be programmed in special registers (RAL1, RAL2) for the low address byte. A
valid address is recognized in case the high and low byte of the address field correspond to one of the compare
values. Thus, the QuadFALC
TM can be called (addressed) with 6 different address combinations. HDLC frames
with address fields that do not match any of the address combinations, are ignored by the QuadFALC
TM.
In case of a 1-byte address, RAL1 and RAL2 are used as compare registers. The HDLC control field, data in the
I-field and an additional status byte are temporarily stored in the RFIFO. Additional information can also be read
from a special register (RSIS).
As defined by the HDLC protocol, the QuadFALC
TM performs the zero bit insertion/deletion (bit stuffing) in the
transmit/receive data stream automatically. That means, it is guaranteed that at least one “0” will appear after 5
consecutive “1”s.
12.1.1
Non-Auto Mode
(MODE.MDS(2:1) = 01
B; MODE2.MDS22.21 =01B; MODE3.MDS32.31 =01B)
Characteristics: address recognition, flag- and CRC generation/check, bit stuffing
All frames with valid addresses are forwarded directly via the RFIFO (RFIFO2, RFIFO3) to the system memory.
12.1.2
Transparent Mode 1
(MODE.MDS(2:0) = 101
B; MODE2.MDS2(2:0) = 101B; MODE3.MDS3(2:0) = 101B)
Characteristics: address recognition, flag- and CRC generation/check, bit stuffing
Only the high byte of a 2-byte address field is compared to registers RAH(2:1). The whole frame excluding the first
address byte is stored in RFIFO (RFIFO2, RFIFO3).
12.1.3
Transparent Mode 0
(MODE.MDS(2:0) = 100
B; MODE2.MDS2(2:0) = 100B; MODE3.MDS3(2:0) = 100B)
Characteristics: flag- and CRC generation/check, bit stuffing
No address recognition is performed and each frame is stored in the RFIFO (RFIFO2, RFIFO3).
12.1.4
SS7 Support
SS7 protocol is supported for channel 1 only by means of several hardware features.