Rigol VG1021

Overview

The Rigol VG1021 is a 20Mhz 100MS/s Function/Arbitrary waveform generator.

Protocol

Device Class code implies compatibility with USBTMC USB488 (USB Class 0xFE, Subclass 0x03, Protocol 0x01)¹, but deviates significantly from specification.^2,3. It fails to heed the "multiple of four" transaction length, sends commands in a nonstandard way and uses reserved bytes that should be zero. Any general purpose USBTMC driver will time out when trying to read an answer from the device, because the command requiring response didn't register as such.

Packet types

Packets seen so far (note that details differ from USBTMC specification):

Name	MsgID or bRequestType	bRequest	Endpoint or wIndex	Description
DEV_DEP_MSG_OUT	1		BULK-Out(0x01)	Prepare for a device dependent command. Header includes command length.
Command			BULK-In(0x82)	Write a command.
REQUEST_DEV_DEP_MSG_IN	2		BULK-Out(0x01)	Request a response for the previous command that requires one.
DEV_DEP_MSG_IN	2		BULK-In(0x82)	Read the response for the previous command that requires one.
Vendor Request 0x09	0xC2	0x09	CTRL_MSG	Unknown vendor endpoint request, wLength = 0x04. So far always returns 01 00 00 00
???TRIGGER???	128		BULK-Out(0x01)	Trigger the device. I'm assuming it's implemented, need to check.

DEV_DEP_MSG_OUT

Consists of a USBTMC DEV_DEP_MSG_OUT header:

Offset	Field	Value	Description
0	MsgID	1	Identifies as DEV_DEP_MSG_OUT.
1	bTag	Number	Per USBTMC specification, bTag is incremented by host every time a USBTMC message is sent. Rolls over from 255 -> 1.
2	bTagInverse	Number	Per USBTMC specification, bTagInverse is the one's complement of bTag.
3	Reserved	0x00	Must be 0x00.
4-7	TransferSize	LSByte first	Length of command without header or alignment bytes.
8	bmTransferAttributes	0x01	EOM, indicating that the last message byte (excluding alignment bytes) in the transfer is the last byte of the message (used for USBTMC Split messages that use multiple transfers. Yet to see one on this device, don't know if it supports them. Probably not.)
9-11	Reserved	0xCDCDCD	According to USBTMC spec, must be 0x000000. I interpret as Command Data to follow.

Command

Consists of a BULK-Out transfer with command without header, leading ":", newline or alignment bytes. Does not follow the PacketSize = n*4 bytes requirement.

REQUEST_DEV_DEP_MSG_IN

Consists of a USBTMC REQUEST_DEV_DEP_MSG_IN header to BULK-Out(0x01) endpoint. The command is not sent with this packet or message, instead, the command is sent using the DEV_DEP_MSG_OUT and Command packets. This packet only requests the response. Consists of a USBTMC Message DEV_DEP_MSG_OUT header:

Offset	Field	Value	Description
0	MsgID	2	Identifies as REQUEST_DEV_DEP_MSG_IN.
1-3	bTag, bTagInverse, Reserved	Number	See #DEV_DEP_MSG_OUT
4-7	TransferSize	LSByte first	Maximum response data bytes. Only seen 0x40.
8	bmTransferAttributes	0x01	According to USBTMC spec, should be 0x02 (use TermChar from byte 9) or 0x00 (ignore TermChar))
9	TermChar	0x0A	See USBTMC spec. For this device, not important.
10-11	Reserved	0x0000	As specified.

DEV_DEP_MSG_IN

Compliant with USBTMC, assuming wMaxPacketLength is 64. Header and data from BULK-In(0x82). If more than 52 bytes of data (plus 12 header) is needed, then rest of the data is sent in following packets without header or alignment bytes, compliant with USBTMC.

Offset	Field	Value	Description
0	MsgID	2	Identifies as DEV_DEP_MSG_IN.
1-3	bTag, bTagInverse, Reserved	Number	See #DEV_DEP_MSG_OUT
4-7	TransferSize	LSByte first	Length of returned data without header or alignment bytes.
8	bmTransferAttributes	0x01	See USBTMC Specifications.
9-11	Reserved	0x0000	As specified.

Vendor Request 0x09

Vendor Endpoint In control message, always returns 0x01000000.

• bmRequestType = 0xC2
• bRequest = 0x09
• wValue = 0x00
• wIndex = 0x00
• wLength = 0x04

Assuming first byte of response to be USBTMC_Status byte⁴.

TRIGGER

*TRG

Transfer sequences

Transfer sequences as performed by bundled software.

Command sequence

1. DEV_DEP_MSG_OUT
2. Command
   • If the command requires no response, the process ends here.
3. Vendor Request 0x09
4. Vendor Request 0x09
5. REQUEST_DEV_DEP_MSG_IN
6. DEV_DEP_MSG_IN

Startup sequence

Here commands are in bold and responses from device in italics. Commands can be abbreviated to uppercase portions (per VISA specifications). Commands are sent and responses read using #Command sequence

1. *IDN? - RIGOL TECHNOLOGIES,VG1021, <serial>,<firmware>
2. SYSTem:BEEPer:STATe ON
3. VOLTage:RANGe:AUTO ON
4. OUTPut:LOAD INFinity
5. OUTPut:POLarity NORMal
6. PHASe 0
7. OUTPut OFF
8. OUTPut:SYNC OFF
9. FREQuency 1000
10. VOLTage 5Vpp
11. VOLTage:OFFSet 0V
12. FUNCtion:SQUare:DCYCle 50
13. FUNCtion::SYMMetry 50
14. PULSe:DCYCle 50
15. FUNCtion:USER EXP_RISE
16. AM:SOURce INTernal
17. AM:DEPTh 100
18. AM:INTernal:FREQuency 100
19. AM:INTernal:FUNCtion SINusoid
20. FM:SOURce INTernal
21. FM:DEViation 100
22. FM:INTernal:FREQuency 100
23. FM:INTernal:FUNCtion SINusoid
24. FSKey:SOURce INTernal
25. FSKey:FREQuency 100
26. FM:INTernal:RATE 100
27. PM:SOURce INTernal
28. PM:DEViation 100
29. PM:INTernal:FREQuency 100
30. PM:INTernal:FUNCtion SINusoid
31. SWEep:SPACing LINear
32. FREQuency:STARt 100
33. FREQuency:STOP 1000
34. SWEep:TIME 1
35. TRIGger:SOURce IMMediate
36. BURSt:NCYCles 1
37. BURSt:PHASe 0
38. TRIGger:SOURce IMMediate
39. BURSt:INTernal:PERiod 0.01
40. TRIGger:DELay 0
41. COUNter:COUPling AC
42. COUNter:HFRState OFF
43. COUNter:SENSitivity HIGH
44. FUNCtion SINusoid
45. FREQuency 1000
46. VOLTage 5Vpp
47. VOLTage:OFFSet 0V
48. AM:STATe? - OFF
49. FM:STATe? - OFF
50. FSKey:STATe? - OFF
51. PM:STATe? - OFF
52. SWEep:STATe? - OFF
53. BURSt:STATe? - OFF
54. FUNCtion SINusoid

References

• ¹ USB.org - Defined 1.0 Class Codes
• ^{2, 4} USB.org - Approved Class Specification Documents - TMC Specifications USBTMC 1.00
• ³ USB.org - Approved Class Specification Documents - TMC Specifications USBTMC-USB488 1.00