Developing a USBTMC-device

[SveinR]

My USBTMC-device under development recognizes a MsgID = REQUEST_DEV_DEP_MSG_IN(equivalent to LabVIEW's VISA READ), but not a MsgID = DEV_DEP_MSG_OUT(VISA WRITE). It seems like the latter MsgID is not sent at all. After a few seconds delay, the host sends the control pipe request INITIATE_CLEAR.

LabVIEW is version 7.1, NI-VISA 3.3.1

If problem description is insufficient, please let me know.

[Jufail]

Hai

I am too developing one TMC device. Can you help me in clearing my small doubt.

I had to send SRQ through interrupt endpoint. In TMC spec they specifies one bitpattern and the status byte to send through interrupt endpoint. But i am little bit confused with the status byte. what they actually menat of this status byte. Can you help me?

Thank you

Jufail

[GPIB_Guru]

With USBTMC, when you need to request service, the device shall do a ReadStatusByte (equivalant to a GPIB Serial Poll) algorithm within the device and return the SRQ AND the status byte to the host using a single interrupt-IN transfer.

Does that make sense?

[Makoto]

Jufail,
The Status Byte documented in USBTMC-USB488 specification is exactly the same entity of what defined in IEEE488.1 std.  For T&M devices having SR1 capabilities, there are two situations for sending out Status Byte stream through the Interrupt-IN endpoint - 1)when the device is queried by READ_STATUS_BYTE class request, and 2)when device's SRQ state has changed from 0 to 1.  The 1st one is a response for READ_STATUS_BYTE request, and the 2nd one is a packet that the device spontaneously sends out.

[Jufail]

Hai Makoto,

Thank you very much for your help.