5.1.4 I2C_WriteRead Command and its Response

The I2C_WriteRead command (0x4A) initiates a combined I²C write followed by an I²C read. The command writes wWrDtLen bytes of vDatPac and then reads wRdDtLen bytes from the I²C client device addressed by bAddress.

This command is sent through Endpoint 0x03 (OUT) and the response is read through Endpoint 0x83 (IN).

If the write data length exceeds the available payload space in the first command packet, additional write data is transmitted using continuation packets. A response is available after each transmitted packet.

Table 5-11. `I2C_WriteRead` - Command
SI. No.	Byte Index	Command		Description
1	0	`0x4A`	Command code	Initiates the I²C write-read transaction
2	1	`bAddress`	I²C client address	7-bit I²C client address
3	2	`L(wWrDtLen)`	Write data length (lower byte)	Number of data bytes to be written; maximum length 65535 bytes
4	3	`H(wWrDtLen)`	Write data length (upper byte)
5	4	`L(wRdDtLen)`	Read data length (lower byte)	Number of data bytes to be read; maximum length 65535 bytes
6	5	`H(wRdDtLen)`	Read data length upper byte	Number of data bytes to be read; maximum length 65535 bytes
7	6	`b0(vDatPac)`	First data byte	The N (up to 58) data bytes Note: The write data length can be up to 65,535 bytes. If the length exceeds 58 bytes, use multiple data packets, as done for I2C_Write.
8	7	`b1(vDatPac)`	Second data byte
9	…	`…`	...
10	n+5	`bn-1(vDatPac)`	The N^th data byte
11	Wait for the first response to determine whether the command was accepted
12	If accepted, continue polling for read data until all requested bytes are received or an error occurs.

Table 5-12. `I2C_WriteRead` - First Response
Byte Index	Response		Description
0	`0x4A`	Return command code	Returns whether the `I2C_WriteRead` command was accepted.
1	`0x22`	Accepted – initiated	The command is accepted, an I²C write is initiated, and then an I²C read is performed.
	`0x60`	Rejected – wrong parameters	The command is rejected because the parameters are invalid
	`0x64`	Rejected – I²C is busy	The command is rejected because the I²C module is busy

Table 5-13. `I2C_WriteRead` - Second Response
Byte Index	Second Response		Description
0	`0x4A`	Return command code	The I²C_WriteRead command is continued
1	`0x21`	I2C_WriteRead is continued	The I²C_WriteRead command is continued
	`0x80`	Failure - address NACK	An address NACK was received. Verify the I²C client address.
	`0x88`	Failure - clock-stretch timeout	A clock-stretch timeout occurred. Recover the bus and retry, if required.
	`0x8C`	Failure - arbitration lost	Bus arbitration was lost
	`0x90`	Failure - an I²C bus error occurred	A bus error occurred
2	`L(wRdDtLen)`	Read data length (lower byte)	Number of data bytes to be read (maximum 65,535 bytes)
3	`H(wRdDtLen)`	Read data length (upper byte)	Number of data bytes to be read (maximum 65,535 bytes)
4	`b0(vDatPac)`	First data byte	The first 60 data bytes are read
5	`b1(vDatPac)`	Second data byte
…	`…`	...
63	`b59(vDatPac)`	The 60^th data byte

Table 5-14. `I2C_WriteRead` - Subsequent Response
Byte Index	Subsequent Response		Description
0	`0x4A`	Return command code	The I²C_WriteRead command is continued
1	`0x21`	The I2C_WriteRead operation is continued	The I²C_WriteRead command is continued
	`0x88`	Failure - clock-stretch timeout	A clock-stretch timeout occurred
	`0x8C`	Failure - arbitration lost	Bus arbitration was lost
4	`b60(vDatPac)`	The 61^st data byte	The next 62 data bytes are read
...	`...`	...
63	`b121(vDatPac)`	The 122^nd data byte
The subsequent response sequence is repeated until all requested bytes have been received or an error occurs