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TC3x Multiplexer User's Guide
8.2.3 Control field
The control field defines the frame type.
Table 8: Coding of the control field
Frame Type
SABM
(Set
Asynchronous
Balanced Mode)
UA
(Unnumbered
Acknowledgement)
DM
(Disconnected Mode)
DISC
(Disconnect)
UIH
(Unnumbered
Information with Header
check)
P/F: Poll/Final bit
Commands: P = 1, Responses: F = 1
For each DLCI, only one frame with P = 1 may ever be expected.
8.2.4 Length indicator
The Length Indicator specifies the length of the following information field.
The length of the Length Indicator can be extended with the E/A bit. The default length is 31 bytes.
1st octet:
Bit 1
E/A
2nd octet:
Bit 1
L8
E/A = 1: only one octet for the Length Indicator
E/A = 0: two octets for the Length Indicator
8.2.5 Information field
The Information Field contains the data and has an octet structure. The field only exists for UIH frames
(Unnumbered Information with Header check).
To transfer information fields, the P/F bit is set to 0; a response is not necessarily expected.
8.2.6 Frame checking sequence field (FCS)
The Frame Checking Sequence (FCS) is computed with the address, control and length fields.
For further information and the specification of the frame checking sequence refer to /2/:
TC3x_UG_01_V03.10 - Released
1
2
3
1
1
1
1
1
0
1
1
1
1
1
0
1
1
1
Bit 2
Bit 3
Bit 4
L1
L2
L3
Bit 2
Bit 3
Bit 4
L9
L10
L11
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4
5
6
1
P/F
1
0
P/F
1
1
P/F
0
0
P/F
0
1
P/F
1
Bit 5
Bit 6
Bit 7
L4
L5
L6
Bit 5
Bit 6
Bit 7
L12
L13
L14
7
8
0
0
1
0
0
0
1
0
1
1
Bit 8
L7
Bit 8
L15
10.01.2002
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