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NXP Semiconductors
UM191812
PN544 C2 User Manual
191812
All information provided in this document is subject to legal disclaimers.
© NXP B.V. 2010. All rights reserved.
User Manual
Rev. 1.2 — 2010-06-16
17 of 172
7.4.3 LLC Header description
The LLC Header (called also SHDLC control field) is part of the LLC frame structure
defined in the following figure:
Fig 8. LLC layer (SHDLC)
7.4.3.1 SHDLC frame types
SHDLC uses several types in order to transfer data and to manage or supervise the
communication channel between the two endpoints (ends of the communication
channel):
I-Frames (Information frames):
Carry upper-layer information and some control
information. I-frame functions include sequencing, flow control, and error detection and
recovery. I-frames carry send and receive sequence numbers.
S-Frames (Supervisory Frames):
Carry control information. S-frame functions include
requesting and suspending transmissions, reporting on status, and acknowledging the
receipt of I-frames. S-frames carry only receive sequence numbers.
U-Frames (Unnumbered Frames):
Carry control information. U-frame functions include
link setup and disconnection, as well as error reporting. U-frames carry no sequence
numbers.
7.4.3.2 Control field
The SHDLC control field has the structure described in following table.
Table 6.
SHDLC Control field coding
Bit Field
Frame Types
8 7 6 5 4 3 2 1
I
1 0
N(S)
N(R)
S
1 1 0 TYPE
N(R)
U
1 1 1
M