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
SHDL
C 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 SHDL
C 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
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