NXP Semiconductors
UM191812
PN544 C2 User Manual
191812
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User Manual
Rev. 1.2 — 2010-06-16
18 of 172
Where:
- N(S): Number of the information frame
- N(R): Number of next information frame to receive
- TYPE: Type of S-Frame
- M: Modifier bits for U-Frame
I-Frames coding
The functions of the information(
I
) command and response is to transfer sequentially
numbered frames, each containing an information field, which might be empty, across the
data link.
S-Frames coding
Supervisory(
S
) commands and responses are used to perform numbered supervisory
functions such as acknowledgment, temporary suspension of information transfer, or
error recovery. Frames with the S format control field do not contain an information field.
Supervisory Format commands and responses are as follows:
RR
: Receive Ready is used by an endpoint to indicate that it is ready to receive an
information frame and/or acknowledge previously received frames.
RNR
: Receive Not Ready is used to indicate that an endpoint is not ready to receive any
information frames or acknowledgments.
REJ
: Reject is used to request the retransmission of frames.
SREJ
: This optional command is not supported by the PN544. If received SREJ is
treated like an erroneous frame.
The type coding is given by the following table:
Table 7.
Type coding of the S-Frames
Frames type
status
RR
00 Mandatory
REJ
01 Mandatory
RNR
10 Mandatory
SREJ
11 Not
supported
Optional type of frame shall not be used before capability negotiation is defined during
initialization.