Functional Description
2.5.8
S- and Q-Channel Access
Access to the received/transmitted S or Q channel is provided via registers. As specified by
CCITT I.430, the Q bit is transmitted from TE to NT in the position normally occupied by the
auxiliary framing bit (F ) in one frame out of 5, whereas the S bit is transmitted from NT to TE
A
in a spare bit, see figure 43.
The functions provided by the ISAC-S are:
TE/LT-T mode:
– Synchronization to the received 20-frame multiframe by means of the received M bit pattern.
Synchronism is achieved when the M bit has been correctly received during 20 consecutive
frames starting from frame number 1 (table 7).
– When synchronism is achieved, the four received S bits in frames 1, 6, 11 and 16 are stored
as SQR1 to SQR4 in the SQRR register if the complete M bit multiframe pattern was
correctly received in the corresponding multiframe. A change in any of the received four bits
(SQR1, 2, 3 or 4) is indicated by an interrupt (CISQ in ISTA and SQC in CIR0).
– When an M bit is observed to have a value different from that expected, the synchronism is
considered lost. The SQR bits are not updated until synchronism is regained. The
synchronization state is constantly indicated by the SYN bit in the SQRR register.
– When synchronism with the received multiframe is achieved, the four bits SQX1 to SQX4
stored in the SQXR register are transmitted as the four Q bits (F
6, 11 and 16 respectively (starting from frame number one). Otherwise the bit transmitted is
a mirror of the received F bit. At loss of synchronism (mismatch in M bit) the mirroring is
A
bit position) in frames 1,
A
resumed starting with the next F bit.
A
Semiconductor Group
100
INFINEON [ Infineon ]
