NXP Semiconductors UM11227 - RF Output Buffer Data Frame; Data Buffer Length; End of Message (EOM); RF Transmission Randomization

NXP Semiconductors
UM11227
NTM88 family of tire pressure monitor sensors
UM11227 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2020. All rights reserved.
User manual Rev. 6 — 24 April 2020
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10.16.2 RF output buffer data frame
When using the RF data buffer mode each frame of data is sent as 2 to 256 bits per
frame with a possible two trailing bits for an end-of-message, EOM, as shown in
Figure 30. The actual data being transmitted in a given data frame and any combinations
of data frames into a single datagram is dependent on the user software.
The number of frames sent in a given datagram can be from 1 to 16 based on the
FNUM[3:0] bits in the RFCR3. The 256-bit buffer is divided into two pages of 128 bits as
selected by the RPAGE bit in the RFCR2.
The data buffer is unloaded to the RF output starting with the least significant bit (RFD0)
in the least significant byte (RFB0) up through the most significant bit (RFD127) in the
most significant byte (RFB15). This is often referred to as "little-endian" data ordering.
256
80
2
Maximum
258-bit format
Minimum
2-bit format
80-bit format
53-bit format
optional EOM
with all byte lengths
80
data in each byte defined by user software
RFBA
RFB0
RFB1 RFB2 RFB3 RFB4 RFB5 RFB6 RFB7 RFB8 RFB9
RFB0
bits [1:0]
RFB6
bits [2:0]
2
E
OM
RFB0 RFB1 RFB2 RFB3 RFB4 RFB5 RFBB RFBC RFBD RFBE RFBF
aaa-028031
RFB0 RFB1 RFB2 RFB3 RFB4 RFB5
2
EOM
Figure 30. Data frame formats
10.16.2.1 Data buffer length
The number of bits sent in a given transmission frame is selected by the FRM[7:0]
control bits encoded as a direct binary number plus one. This gives a range of 2
through 256 bits. Data written to data buffer bits above the highest bit number will be
ignored. Transmission always begins with the data written in the RFB0 location. When
the requested number of bits have been transmitted an interrupt to the MCU can be
generated if the RFIE bit is set.
10.16.2.2 End of Message (EOM)
If the EOM control bit is set, then at the end of the data frame there will be carrier for
a period of two bit times at level high for the OOK modulation modes or f
DATA1
for the
FSK modulation modes. Following the EOM period there will be no carrier for either
the OOK or FSK modes. If the EOM control bit is clear, no EOM period is added to the
transmission.
10.16.3 RF transmission randomization
When there are two or more different transmitters, the clock rates of each may drift into
synchronism with each other; and there is the possibility of RF data collisions and the
loss of data from both transmitters. In order to reduce possible RF data collisions each
transmission will contain from 1 to 16 frames of data. Each frame may be spaced at after
the initially timed transmission start time and between any two data frames.