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Direct mode 1 (bit 6 = 1 in the ISO Control register) uses the subcarrier signal decoder of the selected
protocol (as defined in the ISO Control register). This means that the receive output is not the subcarrier
signal but the decoded serial bit stream and bit clock signals. The serial data is available on I/O_6 (pin 23)
and the bit clock is available on I/O_5 (pin 22). The transmit side is identical; the application has direct
control over the RF modulation through the MOD input. This mode is provided so that the application can
implement a protocol that has the same bit coding as one of the protocols implemented in the reader, but
needs a different framing format.
To use direct mode, first select the direct mode to enter by writing B6 in the ISO Control register. This bit
determines if the receive output is the direct subcarrier signal (B6 = 0) or the serial data of the selected
decoder. If B6 = 1, also define which protocol should be used for bit decoding by writing the appropriate
setting in the ISO Control register.
The reader actually enters the direct mode when B6 (direct) is set to 1 in the Chip Status Control register.
Direct mode starts immediately. The write command should not be terminated with a stop condition (see
communication protocol), because the stop condition terminates the direct mode and clears B6. This is
necessary as the direct mode uses one or two I/O pins (I/O_6, I/O_5). Standard parallel communication is
not possible in direct mode. Sending a stop condition terminates direct mode.
Figure 6-5
shows mode 0 and mode 1 in direct mode.
•
In mode 0, the reader is used as an AFE only, and protocol handling is bypassed.
•
In mode 1, framing is not done, but SOF and EOF are present. This allows for a user-selectable
framing level based on an existing ISO standard.
In mode 2 (standard mode), data is ISO-standard formatted. SOF, EOF, and error checking are removed,
so the microprocessor receives only bytes of raw data through a 12-byte FIFO.
14443A
Mode 2: Full ISO with framing and error checking (typical mode)
Copyright © 2006–2017, Texas Instruments Incorporated
Analog Front End (AFE)
ISO Encoders and Decoders
14443B
15693
Packetization and Framing
Figure 6-5. User-Configurable Modes
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Product Folder Links:
SLOU186G – AUGUST 2006 – REVISED MAY 2017
Tag-it
TRF7960 TRF7961
TRF7960, TRF7961
Mode 0:
Raw subcarrier data
Mode 1:
Unframed raw ISO
formatted data
Detailed Description
21
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