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MCP451WF Datasheet(PDF) 4 Page - Microchip Technology |
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MCP451WF Datasheet(HTML) 4 Page - Microchip Technology |
4 / 50 page MCRF450/451/452/455 DS40232H-page 4 2003 Microchip Technology Inc. To enhance data integrity for writing, the device includes an anti-tearing feature. This anti-tearing feature provides verification of data integrity for incomplete write cycles due to failed communication between the Interrogator and the device during the write sequences. 1.1 Device’s Communication with Interrogator The device can be operated in either Fast Read Request (FRR) or Fast Read Bypass (FRB) mode, depending on the status of bit 31 (FR: bit) of Block 0. If the FR bit is set, the device is operated in FRR mode, and FRB mode, if the FR bit is cleared. The FR bit is always reprogrammable and not write-protectable. The FRR mode is a default setting. The communication between the Interrogator and tag starts with a FRR or FRB command. In FRR mode, the device sends a response only when it receives the FRR command, not the FRB command. Conversely, the device in FRB mode sends a response when it receives the FRB command only, not the FRR command. If the device is set to FRR mode and also set to TTF mode (TF bit = set), the device can send the FRR response as soon as it is energized. One of the main purposes of using the two different modes (FRR and FRB) is to use the device effectively in the item level supply-chain application, where a rapid identification and an effective anti-collision read/write process is needed (i.e., to identify whether it is a paid or unpaid item, or whether it passed one particular point of interest or not). This can be done by either checking the status of the FR bit or by checking the response of the tag to the command. For this reason, the FR bit is also called an Electronic Article Surveillance (EAS) bit. 1.1.1 OPERATION OF TAG IN FRR MODE If the device is in the FRR mode (FR bit = set), the communication between the Interrogator and the device can start in two ways, depending on the status of TF (Bit 30 of Block 0). If the TF bit is cleared, it is called ITF mode. In this case, the tag waits for the Interrogator’s FRR command and sends the FRR response data when it sees the FRR command. If the TF bit is set, the device is in a TTF mode. In this case, the tag sends the FRR response as soon as it is energized, even without the FRR command. The tag has a short listening window (1 ms) immediately after the FRR response. The Interrogator sends its next command during this listening window. The FRR response includes the 32 bits of tag ID and FRF (Blocks 3 -5). See Tables 7-3, 7-4 and 7-6 for data. The Interrogator identifies which tags are in the field by receiving their FRR responses. Based upon the FRR response, the Interrogator will send Matching Code 1 (MC1) or Matching Code 2 (MC2) during the tag’s listening window. The Interroga- tor sends the MC1 to put the tag into Sleep mode. Tags in Sleep mode never respond to any command. Removal of the Interrogator’s RF energy from the device is the only way to wake-up the device. If the tag needs further read/write processing, the Interrogator sends the MC2, followed by a Read or Write command. After the completion of reading or writing of block data, the Interrogator sends an End command to put the tag into Sleep mode. The reading and writing of the FRR devices takes place in the Anti-collision mode. For instance, if there are multiple tags in the field, the Interrogator selects one tag at a time by controlling the tag’s time slot for the FRR response. The Interrogator repeats this sequence until all tags in its field are processed: - send FRR command - receive FRR response - send Matching Code 1 or 2 at tag’s listing window - send Read Block command/or send Write Block command and data - verify read/write response - send End command - verify the End command response - look for other tag’s FRR responses 1.1.2 OPERATION OF TAG IN FRB MODE The communication with the device in the FRB mode is initiated by the FRB command only. If the device sees the Interrogator’s FRB command, it sends its 32-bit tag ID and waits for the MC2. This is followed by a Read or Write command. Once the device is read or written, the Interrogator sends an End command. Unlike the FRR mode, the reading and writing of the tag are processed in a non Anti-collision mode. See Section 6.0 “Read/Write Anti-Collision Logic”, for the read and write anti-collision algorithm. See Example 9-1 for command sequences and device responses. |
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