mt90502ag2 Zarlink Semiconductor, mt90502ag2 Datasheet - Page 39

• Manufacturer Part Number: mt90502ag2
• Description: Multi-channel Aal2 Sar
• Manufacturer: Zarlink Semiconductor

2.2.3
Other than PCM and ADPCM data, MT90502 can also send/receive generic AAL2 CPS-Packets directly to/from
the H.100/H.110 bus. Those CPS-Packets must be encapsulated in HDLC format before they can be put onto
H.100/H.110 bus. The HDLC encapsulation of the data allows an external SSCS engine (e.g., G.723, G.728 or
G.729) to pass over CPS-Packets or CPS-Packet payloads to the MT90502 through TDM bus.
HDLC data is accumulated until a flag is received signifying the end of an HDLC packet (see Section 2.10 on page
101). Then, either bit-wise or byte-wise zero-extraction (configurable for the entire chip in register 500h) is
performed on the HDLC data. At this stage, the HDLC packets can be re-formatted as AAL2 CPS-Packets for
treatment by the TX SAR.
2.2.3.1
Any number from 1 to 128 of consecutive time slots on a single H.100/H.110 stream can be grouped as a single
HDLC stream to carry HDLC packets. For each TSST, an entry in TX CAM lists the HDLC stream number
associated with that TSST; these stream numbers are the same for all TSSTs carrying data for a single HDLC
stream. Within a single HDLC stream, one or more HDLC channels can be transported. An HDLC channel carries
CPS-Packets destined to the same AAL2 channel. Up to 1023 channels, whether they are xxPCM channels or
HDLC channels, are supported by MT90502.
Each HDLC stream must be assigned N consecutive assembly structures in TX TDM Control Memory, as seen in
Figure 13, “HDLC CPS-Packet Assembly Structure,” on page 40. N is always the same as the number of HDLC
channels carried by that HDLC stream with only one exception, that is, when the number of HDLC channels is one,
and the TSSTs occupied by the HDLC stream is more than one, N must be 2.
2.2.3.2
HDLC packets may contain zero, one, or two address bytes that immediately follow the start flag. For HDLC
packets containing one or two address bytes, the last address byte can be used to indicate a channel number. If
the last address byte is used to indicate a channel number, each of the 256 possible channel numbers can be
directed to a different CPS-Packet final assembly structure. Each CPS-Packet, based on its HDLC channel
number, can be directed to a different VC/CID. If the value of the last address byte exceeds the allowed number of
HDLC channels for that HDLC stream, the channel number 0 will be used for that CPS-Packet. All address bytes
not used to indicate a channel number are discarded by the TX TDM module and do not appear in an AAL2
CPS-Packet. The HDLC stream number added to the HDLC address byte will yield the HDLC channel number.
Whether or not the address byte(s) will be used to indicate a channel number is determined independently for each
HDLC stream using the “Header Type” field of the HDLC CPS-Packet assembly structure (see Figure 13 on
page 40).
Treatment of HDLC Data
HDLC Streams
Address Bytes
Zarlink Semiconductor Inc.
MT90502
39
Data Sheet