NXP Semiconductors UM11227 - Initial Time Interval; Interframe Time Intervals

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
108 / 205
t0
time not to scale
aaa-028032
Space intervals have no carrier frequency output, equivalent to data = 0 and may have the
RFM crystal oscillator, VCO and PLL turned off by the IFPD bit.
SPACESPACE SPACE
Interframe intervals
1 to 16 data frames
with identical data
Start of time
interval for
datagram
DATA FRAME DATA FRAME DATA FRAME
t
DATA
Initial interval
Figure 31. Radio frequency transmission randomization
The generation of the initial and interframe time intervals can be done with a combination
of a programmable counter, a pseudo-random interval generator and a frame counter.
The initial time interval can be done by adjusting the start time using the MCU or using
this interval timing generator.
time not to scale
aaa-028033
Interframe interval 1 Interframe interval 2
t0
Start of time
interval for
datagram
Initial interval
t
BASE
40 × t
RAND
t
RAND
t
FN
t
RAND
t
BASE
, t
RAND
and t
FN
may be all zero in the initial interval.
t
BASE
, t
RAND
and t
FN
may be all zero in an interframe interval.
All interframe intervals may have different t
BASE
, t
RAND
and t
FN
times.
t
BASE
t
BASE
t
FN
Figure 32. Radio frequency transmission initial and interframe time intervals
10.16.3.1 Initial time interval
When generating an initial time interval, the MCU loads the RFM interval generator
variables and enters the STOP1 mode. When the initial time interval ends, the data
in the RFM data buffer is automatically sent and the MCU will wake at the end of the
transmission. The initial time interval is made up of two components:
t
INIT
= t
BASE
+ (40 × t
RAND
)
Where:
t
INIT
= Total time interval before first frame is transmitted in ms
t
BASE
= Base time in ms; ≤5 ms not recommended
t
RAND
= Pseudo-random time in ms based on a Galois 7-bit LFSR
10.16.3.2 Interframe time intervals
When generating an interframe time interval the MCU loads the RFM interval generator
variables and then goes to the STOP1 mode. When the interframe time interval ends the