A-14
A2
ICS’s Application Note AB80-4 for more detailed information on RPC SRQ
programming and interrupt handling.
A2.4 Transferring Data
ICS's 80xx Interfaces normally transfer small amounts of data so there are no
data transfer problems. However, when reading, the user should not attempt to
limit the amount of data in a read operation from an 80xx Interface unless the
Interface specifically allows it. Otherwise, the unread data will be discarded.
NB
Reading 10 bytes in a 22 byte data message will result in the loss
of the last 12 bytes.
The 80xx series Interfaces have a
maxRecvSize
of 1024 bytes that limits the
amount of the data that can be transferred in device_write RPC operation.
maxRecvSize
is the last parameter returned when the link is created to the 80xx
by the create_link function.
The user can transfer larger amounts of data or long commands to the 80xx by
dividing the data size by the
maxRecvSize
and then sending
maxRecvSize
blocks
of data until all of the data has been transferred. The device_write function
has a flags parameter which is used to determine whether an END indicator
(EOI) shall be set at the completion of the write operation. The END indicator
(EOI) is only asserted on the last packet. The 80xx does not terminate a write
operation until it receives a packet with the end condition set.
Reading large amounts of data from a GPIB device works the same way. The
80xx does not terminate a read operation until the end condition is met. There
is no readdressing of the GPIB device between packets when multiple packets
are used to transfer large amounts of data. The client can request a read of
more than the maxRecvSize number of bytes but the 80xx will only send a
packet with 1024 bytes and with no reason bits set if there is more data to be
sent. The client continues reading packets until it receives a packet with one
or more reason bits set. See VXI-11 Rule B.6.23.
A2.5 An Example VISA Program
VXI-11.3 Instruments like the 80xx series Interface can be programmed by
making calls to a VISA library. VISA calls are currently the easiest way to
program VXI-11.3 Instruments in a Windows environment. The following C
language example applies to all VXI-11 compliant VISA libraries.
