Texas Instruments TRF7970A Instruction Manual page 46

TRF7970A
SLOS743K – AUGUST 2011 – REVISED APRIL 2014
Step 5: Transmit Data Using Direct Mode
The application now has direct control over the RF modulation through the MOD input (see
The microcontroller is responsible for generating data according to the coding specified by the particular
standard. The microcontroller must generate SOF, EOF, Data, and CRC. In direct mode, the FIFO is not
used and no IRQs are generated. See the applicable ISO standard to understand bit and frame
definitions. As an example of what the developer sees when using DM0 in an actual application,
30 is presented to clearly show the relationship between the MOD pin being controlled by the MCU and
the resulting modulated 13.56-MHz carrier signal.
Step 6: Receive Data Using Direct Mode
After the TX operation is complete, the tag responds to the request and the subcarrier data is available on
pin I/O_6. The microcontroller needs to decode the subcarrier signal according to the standard. This
includes decoding the SOF, data bits, CRC, and EOF. The CRC then needs to be checked to verify data
integrity. The receive data bytes must be buffered locally.
As an example of the receive data bits and framing level according to the ISO14443A standard is shown
in Figure 6-31 (taken from ISO14443 specification and TRF7970A air interface).
46 Detailed Description
TRF7970A
MOD
(Pin 14)
I/O_6
(Pin 23)
Figure 6-29. Direct Control Signals
Figure 6-30. TX Sequence Out in DM0
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Microcontroller
Drive the MOD pin
according to the data coding
specified by the standard
Decode the subcarrier
information according
to the standard
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TRF7970A
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Figure 6-29).
Figure 6-