6.1.4 SPI_Exchange Command and its Response

The SPI_Exchangecommand (0x2C) initiates a full-duplex SPI transaction. The command writes wDatLen bytes from vWrDtPac to the SPI client device while simultaneously reading wDatLen bytes.

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

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

Table 6-11. `SPI_Exchange` - Command
Serial No.	Byte Index	Command		Description
1	0	`0x2C`	Command code	Initiates a full-duplex SPI transaction
2	1	`0xAF`	Command code extension byte	Initiates a full-duplex SPI transaction
3	2	`L(wDatLen)`	Data length (lower byte)	Number of data bytes. Maximum length: 65,535 bytes.
4	3	`H(wDatLen)`	Data length (upper byte)	Number of data bytes. Maximum length: 65,535 bytes.
5	4	`b0(vWrDtPac)`	First data byte	The first 60 bytes
6	5	`b1(vWrDtPac)`	Second data byte
7-63	6-62	...	...
64	63	`b59(vWrDtPac)`	The 60^th data byte
65	Wait for the first response from the MCP2222 to determine whether the command is accepted. If the data length is more than 60 bytes, continue writing.
66		`0x2C`	Repeat command code	The exchange is continued
67	1	`0xA0`	The exchange is continued	The exchange is continued
68	2	`b60(vWrDtPac)`	The 61^st data byte	The next 62 data bytes
69-126	...	...	Additional data bytes
127	63	`b121(vWrDtPac)`	The 122^nd data byte
128	Wait for the next response, which includes the data bytes read, and read them
129	If all data bytes are not written, continue writing, by repeating the above steps from serial number 66 to 128 until all data bytes are written. The final packet may contain fewer than 62 data bytes.
130	Read the final response

Table 6-12. `SPI_Exchange` - First Response
Byte Index	Response		Description
0	`0x2C`	Returns command code	Returns whether the `SPI_Exchange` command was accepted
1	`0x22`	Accepted – initiated	The command is accepted, and a full-duplex SPI transaction is initiated
	`0x60`	Rejected – wrong parameters	The command is rejected because parameters are invalid
	`0x64`	Rejected – SPI is busy	The command is rejected because the SPI module is busy

Table 6-13. `SPI_Exchange` - Second Response
Byte Index	Response		Description
0	`0x2C`	Returns command code	The SPI full-duplex transaction is continued
1	`0x21`	Exchange is continued	The SPI full-duplex transaction is continued
2	`L(wDatLen)`	Data length (lower byte)	Number of data bytes. Maximum length: 65,535 bytes
3	`H(wDatLen)`	Data length (upper byte)	Number of data bytes. Maximum length: 65,535 bytes
4	`b0(vRdDtPac)`	First data byte	The first 60 bytes are read
5	`b1(vRdDtPac)`	Second data byte
...	...	...
63	`b59(vRdDtPac)`	The 60^th data byte

Table 6-14. `SPI_Exchange` - Subsequent Response After Packet Data is Read
Byte Index	Response		Description
0	`0x2C`	Return command code	The SPI full-duplex transaction is continued
1	`0x21`	Exchange is continued	The SPI full-duplex transaction is continued
2	`b60(vRdDtPac)`	The 61^st data byte	The next 62 data bytes are read
...	...	...
63	`b121(vRdDtPac)`	The 122^nd data byte
The subsequent response sequence is repeated until all requested bytes have been exchanged