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I am struggling to understand how do I get a pulse interval encoding scheme implemented in terms of hardware. Is there any source of information available explaining the circuit diagram of the same?

I am using a S2LP transceiver IC and it supports Manchester, NRZ, FEC and 3 out of 6 encoding schemes but I would like to use PIE encoding scheme instead.

Any help/suggestions would be appreciated.

Nilesh

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  • \$\begingroup\$ There is no good reason to use PIE modulated RF and no PIE solution with that IC. \$\endgroup\$ Commented Feb 18, 2021 at 7:49
  • \$\begingroup\$ well, yes but RFID tag protocols asks for it, the very reason I am trying to understand/learn it. \$\endgroup\$ Commented Feb 18, 2021 at 9:25
  • \$\begingroup\$ Ok. Then skewed DC protocol there is used to diode clamp a DC charge to power the Rx so it could Tx a burst reply.. The Rx burst length then determines the binary value. \$\endgroup\$ Commented Feb 18, 2021 at 14:47
  • \$\begingroup\$ @TonyStewartEE75 I have managed to achieve PIE encoding through MCU but now I am trying to understand if the encoded data can be sent via SPI to Tranciever IC? Or will the clocking of SPI alter the meaning of encoded data? \$\endgroup\$ Commented Apr 5, 2021 at 5:19
  • \$\begingroup\$ SPI is synchronous Clk and data will add jitter to the PIE signal and affect integrity. You must define all the variables and decode the way you encoded or use suitable h/w. Pls define your PIE or e-PIE signals. Also Miller or enhanced Miller with 4-ary modulation .. \$\endgroup\$ Commented Apr 5, 2021 at 10:35

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how do I get a pulse interval encoding scheme implemented in terms of hardware

In a practical way? The hardware will be an FPGA or an MCU. The actual implementation will be in Verilog or VHDL for the FPGA, or using your favorite programming language for the MCU. Some MCUs have I/O offload blocks, e.g. the PIO block of the RP2040. Those blocks are programmed using specialized assembly language, or using HDL if they are small embedded PLDs rather than state machines. Whether you'll want to use an I/O offload block depends on how flexible and efficient are the peripherals on the MCU.

For a hobby project you of course could make a PIE encoder and decoder using discrete logic, but that won't make sense for a product other than something boutique where quirkiness of implementation is a selling point.

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Are you actually sure that transceiver handles the encoding you want to use? it isn't mentioned in the datasheets.

Some transceiver (TI ones, for example) have a bypass mode (or test mode) where you can disable the digital modulator and directly drive the RF section with an external digital signal. Then you use an MCU/FPGA/whatever to create the encoding you need (usually you are restricted to OOK/CW for RF encoding).

The ST chip you mentioned seems to have a test mode for continuous transmission or pseudorandom modulation (useful for testing the RF stages) but no such bypass operation mode. There is a direct polar mode (only for TX), are you referring to that?

If you really need to use PIE I'd suggest to use another transceiver or simply ask directly to ST (good luck with that, in my experience)

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  • \$\begingroup\$ I talked with ST guys and got the answer that one can use Direct through the GPIO option for Tx, with an external encoding of the data. Now, I have a question about whether it is possible to use PWM pins of the STM32L152RE to make an encoding in PIE format? As I understood the PWM only offers to change the duty cycle of the different logical levels but not the length? Or on other hand, can one make the encoding in C as my data rate is 125 kbps and the cock is operating at 25 MHz? Any suggestions? \$\endgroup\$ Commented Feb 24, 2021 at 5:00
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Not directly related but perhaps useful, from the experts at Magellan Technology, an Australian firm that has been developing innovative RFID products for 15 years. Here is the response from one of the company’s engineers: “PIE is used in UHF RFID systems where the disadvantages of its relatively low data rate and poor spectral occupancy are balanced against the advantages of continuously supplying power to the tag and the simplicity of detection circuits required on the tag. “PIE encoding is based on a given minimum pulse duration or interval called a Tari, which is named after the ISO 18000-6 Type A Reference Interval. The Tari length is the minimum pulse width for the data 0 symbol. The data 1 symbol, as well as special symbols like Start Of Frame (SOF) and End Of Frame (EOF), are composed of differing numbers of Tari periods.

“The jitter performance is set by the ability to distinguish between the respective symbol Tari lengths. In principle, this would be half the relative Tari length between symbols.

For example, with a data 0 symbol length of 1 Tari and a data 1 symbol length of 1.5 Tari, the maximum allowable jitter would be +0.25 Tari for the data 0 symbol and -0.25 Tari for the data 1 symbol.

These represent best-case values, and are expected to reduce depending upon the detection and decoding circuits used on the tag.” —Mark Roberti, Founder and Editor,RFID Journal

This is different but shares certain aspects of other baseband encoder/decoders commonly used in floppy and hard disk drive (HDD) coding originally used called Modified Frequency Modulation or MFM where data is encoded by simple logic with 1f and 2f resulting a lower transition rate but limited to 1T, 1.5T and 2T. During the 80’s HDD’s used this method at 10Mbps with the clock encoded with the data. Later data rates increased with the modulation scheme changed to RLL 2,7 (Run-Length-Limited)such that the data edge intervals were limited by this range using both edges of the clock. i.e. 2 Clks edges = 1 baud min and 7 Clk edge intervals max with multiple data bits encoded sequentially to reduce the transition rate of recorded edges. (Now much faster and different RLL codes are used)

This is just and example to show how PIE is similar to the RLL pulse intervals are recorded and transferred magnetic recording controllers. Now of course all the encoder, decoders are embedded in the HDD’s and serial data is sent by Serial ATA (Serial Advanced Technology Attachment or SATA to the host.

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