6.1.3 SPI_Read Command and its Response

The SPI_Read command (0x28) initiates an SPI read transaction. The command reads wDatLen bytes of data from the SPI client device selected by the active SPI configuration.

This command is sent through Endpoint 0x06 (OUT). The response is read through Endpoint 0x86 (IN).

If the read data length exceeds the payload capacity of a single USB packet, multiple packets are used. The first packet contains up to 60 data bytes, and each additional continuation packet contains up to 62 data bytes.

Depending on the requested read length, multiple response packets may be returned. The first data response may contain up to 60 bytes, and subsequent response packets may contain up to 62 bytes each.

Table 6-7. `SPI_Read` - Command
Byte Index	Command		Description
0	`0x28`	Command code	Initiates the SPI read transaction
1	`0xAF`	Command code extension byte	Initiates the SPI read transaction
2	`L(wDatLen)`	Data length (lower byte)	Number of data bytes. Maximum length: 65535 bytes.
3	`H(wDatLen)`	Data length (upper byte)	Number of data bytes. Maximum length: 65535 bytes.
Wait for the first response from the MCP2222 to determine whether the command is accepted
If accepted, continue reading until the required number of bytes are read

Table 6-8. `SPI_Read` - First Response
Byte Index	Response		Description
0	`0x28`	Return command code	Returns whether the `SPI_Read` command was accepted
1	`0x22`	Accepted – initiated	The command is accepted, and an SPI read is initiated
	`0x60`	Rejected – wrong parameters	The command is rejected because the parameters are invalid
	`0x64`	Rejected – SPI is busy	The command is rejected because the SPI module is busy

Table 6-9. `SPI_Read` - Second Response
Byte Index	Response		Description
0	`0x28`	Return command code	The SPI read is continued
1	`0x21`	Read continued	The SPI read is continued
2	`L(wDatLen)`	Data length (lower byte)	Number of data bytes to be read (maximum 65,535 bytes)
3	`H(wDatLen)`	Data length (higher byte)	Number of data bytes to be read (maximum 65,535 bytes)
4	`b0(vDatPac)`	First data byte	The first 60 bytes are read
5	`b1(vDatPac)`	Second data byte
...	...	...
63	`b59(vDatPac)`	The 60^th data byte

Table 6-10. `SPI_Read` - Subsequent Response
Byte Index	Response (Endpoint 0x86)		Description
0	`0x28`	Return command code	The SPI read is continued
1	`0x21`	Read continued	The SPI read is continued
2	`b60(vDatPac)`	The 61^st Data Byte	The next 62 data bytes are read
...	...	...
63	`b121(vDatPac)`	The 122^nd Data Byte
Repeat the subsequent response sequence until all requested bytes have been received.