參數(shù)資料
型號(hào): AM79C32A
廠商: Advanced Micro Devices, Inc.
英文描述: Digital Subscriber Controller⑩ (DSC⑩) Circuit
中文描述: 數(shù)字用戶控制器⑩法(DSC⑩)電路
文件頁(yè)數(shù): 37/101頁(yè)
文件大?。?/td> 1607K
代理商: AM79C32A
Am79C30A/32A Data Sheet
37
that a flag sequence is not repeated within the flag
boundaries of the frame, a logical 0 bit is automatically
inserted after each sequence of five contiguous logical
1s. When receiving, the DLC examines the frame con-
tent between the opening and closing flags and auto-
matically discards the first logical 0 which directly
follows five contiguous logical 1s.
D-Channel Address Recognition
The address field, shown in Figure 4, allows for three
types of addresses:
1. 1-byte address signified by the LSB of the first ad-
dress byte being set to a logical 1
2. 2-byte address signified by the LSB of the first ad-
dress byte being set to a logical 0, and the LSB of
the second address byte being set to a logical 1
3. More than 2-byte address signified by the LSB of
both the first and second address bytes being set to
a logical 0
In the case of the LAPD operating environments, the
address is a 2-byte address where the first byte is anal-
ogous to the Service Access Point Identifier (SAPI) and
the second byte is analogous to the Terminal Endpoint
Identifier (TEI) as defined by the CCITT recommenda-
tions.
The DLC is able to recognize D-channel addresses of
all of the three types outlined above. Note that only the
first two bytes of a more than 2-byte address can be
checked by the DLC. There are four First Received
Byte Address Registers (FRARs) which hold the values
used to match against the first byte of the incoming ad-
dress. Similarly, there are four Second Received Byte
Address Registers (SRARs) which hold the values
used to match against the second byte of the incoming
address.
FRAR4 defaults to FE hex; SRAR4 defaults to FF hex.
This default is analogous to the broadcast address de-
fined by the CCITT recommendations. The type of ad-
dress recognition which is enabled is shown in Table 38
Figure 4.
Level-2 Frame Structure Formats
8
7
6
5
4
3
2
1
OCTET 2
OCTET 3
SAPI
TEI
EA=1
EA=0 C/R
FLAG
ADDRESS
CONTROL
FCS
FLAG
01111110
16 bits
8 bits
16 bits
01111110
1
2,3
4
5,6
7
OCTET
FLAG
01111110
1
ADDRESS
16 bits
2,3
CONTROL
8 bits
4
INFORMATION
N bits
5 …
FCS
16 bits
N – 1
FLAG
01111110
N
OCTET
Minimum Packet
General
Notes:
EA = Address Field Extension bit
SAPI = Service Access Point Identifier
FCS = Frame Check Sequence
C/R = Command/Response Field bit
TEI = Terminal Endpoint Identifier
09893H-4
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