ICS N4865A, Instruction Manual

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asserted on the last byte. When the data size exceeds the N4865A's GPIB talk
buffer, the N4865A outputs the fi rst buffer of data to the GPIB bus and sends
an additional device_read RPC to the oscilloscope to read the next buffer's device_read device_read
worth of data. This process repeats until all of the data has been read from the
companion oscilloscope and the N4865A receives a response data packet with
END asserted. If the companion oscilloscope returns a zero length response,
the N4865A will not have any data for the GPIB bus and the GPIB read opera-
tion will timeout.
When the N4865A is addressed to talk and has received a response packet with
END asserted, it will not fetch additional data from the companion oscilloscope
until it has been addressed to listen and sent a device message, a GPIB Device
Trigger, a GPIB Device Clear command or an Interface Clear.
When the N4865A is transistioned to the Listen Active State from the Talk
Active State, it discards any data in the GPIB talk buffer. Similarly, when the
N4865A is transistioned to the Talk Active State from the Listen Active State,
it discards any data left in the GPIB listen buffer.
If the N4865A receives a Service Request from the oscilloscope over the
Reverse Interrupt channel, the N4865A will query the oscilloscope's Status
Byte Register with a read_statusstb RPC when it is safe to do so. If bit 6 in
the Status Byte is set, the N4865A will assert the SRQ line on the GPIB bus
and turn on its front panel SRQ LED. If the N4865A is Serial Polled, it will
immediately output the oscilloscope's Status Byte when addressed to talk.
The SRQ line will be deasserted and the SRQ LED will be turned off. Future
register queries and the response to the Service Request are dependent upon
the program in the GPIB Controller.
The N4865A periodically queries the companion oscilloscope's Status Byte to
update its own Status Byte at a low 3 Hz rate. If the N4865A discovers that the
oscilloscope is no longer asserting its MSS bit, then the N4865A will deassert
the SRQ signal on the GPIB bus and turn off its SRQ LED. The N4865A's
SRQ signal turn off will lag behind the companion oscilloscope due to the
N4865A's low query rate and the user's program.
Status Byte queries are inhibited if the N4865A was addressed to listen and a
device message was written to the companion oscilloscope, to avoid corrupt-
ing any expected oscilloscope response. Status Byte queries resume when the
N4865A has fi nished outputting response data, after a GPIB Device Clear or
a GPIB Device Trigger command or after an Interface Clear.