Rainbow Electronics DS2181A - Manual (Page 10)

DS2181A
041995 10/32
RCR: RECEIVE CONTROL REGISTER Figure 6
(MSB) (LSB)
– – RSM CMSC CMRC FRC SYNCE RESYNC
SYMBOL POSITION NAME AND DESCRIPTION
– RCR.7 Reserved; must be 0 for proper operation.
– RCR.6 Reserved; must be 0 for proper operation.
RSM RCR.5 Received Signalling Mode
0 = Channel Associated Signalling (CAS).
1 = Common Channel Signalling (CCS).
CMSC RCR.4 CAS Multiframe Sync Criteria
0 = Declare sync when fixed sync criteria met.
1 = Declare sync when fixed criteria are met and two additional consecutive
valid multiframe alignment signals are detected.
CMRC RCR.3 CAS Multiframe Resync Criteria
0 = Utilize only fixed resync criteria.
1 = Resync if fixed criteria met and/or if two consecutive timeslot 16 words
have values of 0 in the first four MSB positions (0000xxxx).
FRC RCR.2 Frame Resync Criteria
0 = Utilize only fixed resync criteria.
1 = Resync if fixed criteria met and/or if bit 2 in timeslot 0 of non-align frames
is received in error on three consecutive occasions.
SYNCE RCR.1 Sync Enable
If clear, the synchronizer will automatically begin resync if error criteria are
met. If high, no auto resync occurs.
RESYNC RCR.0 Resync
When toggled low to high, the receive synchronizer will initiate immediately.
The bit must be cleared, then set again for subsequent resyncs.
CEPT FRAME STRUCTURE
The CEPT frame is made up of 32 8-bit channels (time-
slots) numbered from 0 to 31. The frame alignment sig-
nal in bit positions 2 through 8 of timeslot 0 of every other
frame is independent of the various multiframe modes
described below. Outputs TAF and RAF indicate frames
which contain the alignment signal. Timeslot 0 of frames
not containing the frame alignment signal is used for
alarm and national data. See the separate DS2181A
CEPT Transceiver Application Note for more details.
CAS SIGNALLING
CEPT networks support Channel Associated Signalling
(CAS) or Common Channel Signalling (CCS). These
signalling modes are independently selectable for
transmit and receive sides.
CAS (selected when TCR.5 = 0 and/or when RCR.5 = 0)
is a bit-oriented signalling technique which utilizes a
16-frame multiframe. The multiframe alignment signal
(0-hex), extra and alarm bits occupy timeslot 16 of frame
0. Timeslot 16 of the remaining 15 frames is reserved for
channel signalling data. Four signalling bits (A, B, C and
D) are transmitted once per multiframe as shown in Fig-
ure 7. Input TMSYNC establishes the transmitted CAS
multiframe position. Signalling data can be sourced
from input TSD (TCR.6 = 1) or multiplexed into TSER
(TCR.6 = 0).