ICS ELECTRONICS 9099, Инструкция по эксплуатации

Страница: 126 / 178

A-14
A2
A2.4 Transferring Data
ICS's 80xx and 90xx Interfaces normally transfer small amounts of data so
there are no data transfer problems. However, when reading, the user should
not limit the amount of data in a read operation unless the Interface specifically
allows it. Otherwise, the unread data will be discarded.
Nb In 80xx devices, Reading 10 bytes in a 22 byte data message will
result in the loss of the last 12 bytes.
The 80xx and 90xx series Interfaces have a maxRecvSize of 1024 bytes that
limits the amount of the data that can be transferred in device_write RPC op-
eration. 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 interface
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 func-
tion 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 interface 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
interface 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 inerface 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 and 90xx series Interfaces 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.
// Program:
// The purpose of this program is to perform a continuous temp
// query of a Watlow device using a VISA resource. Pass in the
// VISA resource name via the command line. The easiest is to use