P9242-R3/RB Datasheet

© 2019 Integrated Device Technology, Inc.

23

May 17, 2019

9. Bi-Directional User Data Communication

In customer-end systems, the transmitter and receiver boards must have an external microcontroller (MCU) or leverage an existing, onboard

application processor to orchestrate bi-directional communication. Using the I2C communication, the MCU on the transmitter board loads the

user data into specific registers and triggers the communication. The P9242-R3 sends the data to the P9221-R3 using frequency shift keying

(FSK) modulation. The P9221-R3 will receive the data and interrupt the MCU on the receiver when the data is ready to be read. The external

MCU on the receiver follows the same procedure to send the data to the P9242-R3 using amplitude-shift keying (ASK) modulation. When new

data is available to read, the P9242-R3 will interrupt the external MCU on the transmitter board.

Bi-directional user data communication is enabled only in the power transfer phase of the WPC standard. The external MCU on the transmitter

board can read the State register 06E0HEX to determine whether the P9242-R3 is in the power transfer phase. Register 06E0HEX will be set to

09HEX when the device is in the power transfer phase.

See Figure 26 for a state diagram that illustrates the procedure that the external MCU on the transmitter board follows when sending the user

data from the P9242-R3 to the P9221-R3 as described in section 9.1. See Figure 27 for a state diagram that illustrates the procedure that the

external MCU on the transmitter follows to read the data received by the P9242-R3 from the P9221-R3 as described in section 9.2.

9.1 Transferring Data from the P9242-R3 to the P9221-R3

The external MCU on the transmitter board should read bit 0 in register 0800HEX in the P9242-R3 to determine the status of the communication

channel before initiating a new transfer. If the communication channel is free, bit 0 in register 0800HEX is set to 0 BIN. If the communication

channel is busy, bit 0 in register 0800HEX is set to 1 BIN.

The P9242-R3 provides registers 0805HEX to 080EHEX for 10 bytes of outgoing user data loaded by the external MCU on the transmitter board;

however, the P9242-R3 can send only 2 bytes of information at a time and the P9221-R3 can receive only 2 bytes at a time. If the external

MCU on the transmitter loads more than 2 bytes into the outgoing data registers, the P9242-R3 will take 2 bytes of information at a time starting

with register 0805 HEX and send the user data consecutively.

Important: When the P9242-R3 is sending multiple bytes of information consecutively, the external MCU on the receiver must monitor the

transmission very closely and must read incoming data immediately after the interrupt is received to prevent data corruption. The P9221-R3

does not reject new incoming data because old data was not read by the external MCU on the receiver.

The external MCU on the transmitter should write an even number of data bytes to outgoing data registers 0805HEX to 080EHEX and set the

number of bytes to be transferred in the register 0800HEX bits [6:3] accordingly. If the external MCU on the transmitter is sending an odd number

of bytes of user data, it must add one more byte of zeros or a padding byte and write an even number of registers to the outgoing data registers.

For example, if the external MCU on the transmitter is transferring 3 bytes of information, it should add one byte of zeros as the fourth byte,

write the 4 bytes to registers 0805HEX to 0808HEX, and set register 0800HEX bits [6:3] to 0001BIN. The P9242-R3 will not transfer the registers

0809HEX to 080EHEX when the register 0800HEX bits [6:3] are set to 0001BIN.

Table 10. Registers Used for Data Transmission from the P9242-R3 to the P9221-R3

Register Name

Register Address

Command register

0800HEX

Outgoing user data

registers

0805HEX to 080EHEX

(10 bytes)

State register

06E0HEX

The P9242-R3 does not add any checksum to the user data. The external MCU on the transmitter must construct a data packet with the user

data, checksum, header, and other helpful information and load it into the outgoing user registers. For example, if the external MCU on the

transmitter is sending 2 bytes of user data, it must load at least 4 bytes (header byte, checksum byte, and 2 user data bytes) into the outgoing

user data registers. This will help the external MCU on the receiver to decode the data. Figure 24 shows the recommended message structure,

which is consistent with the WPC standard.