Analog Front End (AFE)
ISO15693 Encoders and Decoders
Packetization and Framing
Microcontroller
Direct Mode 0:
Raw RF Subcarrier
Data Stream
Direct Mode 1:
Raw Digital ISO Coded
Data Without
Protocol Frame
ISO Mode:
Full ISO Framing
and Error Checking
(Typical Mode)
37
SLOS757G – DECEMBER 2011 – REVISED MARCH 2020
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Detailed Description
Copyright © 2011–2020, Texas Instruments Incorporated
6.12.7 Direct Mode
Direct mode lets the reader be configured in one of two ways:
Direct mode 0 (bit 6 = 0, as defined in ISO Control register) lets the application use only the front-end
functions of the reader, bypassing the protocol implementation in the reader. For transmit functions, the
application has direct access to the transmit modulator through the MOD pin (pin 14). On the receive
side, the application has direct access to the subcarrier signal (digitized RF envelope signal) on I/O_6
(pin 23).
Direct mode 1 (bit 6 = 1, as defined in ISO Control register) uses the subcarrier signal decoder of the
selected protocol (as defined in 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 select direct mode, first choose which 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, then the application must 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 and I/O_5). Normal parallel communication
is not possible in direct mode. Sending a stop condition terminates direct mode.
shows the different configurations available 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, 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.
Figure 6-26. User-Configurable Modes
