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1260-145 User Manual
Racal Instruments
2003
Module Operation 3-7
illustration purposes, from our example base A24 address
computed earlier, the following absolute addresses would apply for
the operations indicated:
205C01
Read or write to register controlling relays
0-3 and 100-103
205C0D
Read or write to register controlling relays
3000-3003 and 3100-3103
Writing to a control register location is a straightforward process.
Setting a bit high in a control register causes the appropriate relay
to close and setting the same bit low causes the relay to open.
Because of the hardware architecture used in the 1260-145, a
control register written to with a value will be
inverted
(one’s
complement) when read back.
It is especially important to realize that a single write operation to a
control register will affect eight relays simultaneously. Therefore if
only a single bit change is desired, the following process must be
observed.
1.
Read the register first, inverting the bit pattern if necessary
2.
Mask the appropriate bit with an ‘AND’ operation and a byte
mask with all undesired bits set to a ‘1’ and the desired bit
set to a ‘0’ or ‘1’ depending on whether the bit is to be set or
cleared in the desired register
3.
Write the masked data back into the register
As simple as this may seem, a number of products reported as
faulty and sent back for repair are nothing more than the result of
inappropriate register accesses.
The message-based descriptors (
MBC
) provided in
Figures 3-5
through
3-11
are not directly relative to register-based operation.
They do, however, serve a secondary purpose in register-based
operation. In addition to specifying an exact relay (i.e. relay 1000),
the syntax of the message-based descriptor indicates which matrix
the relay belongs to, and the column and row numbers which
intersect the relay position.
Figure 3-4
identifies for each 1260-
145 variant how to interpret the message-based descriptor to
determine these parameters.
The VISA I/O library may be used to control the module. The VISA
function viOut8() is used to write a single 8-bit byte to a control
register, while viIn8() is used to read a single 8-bit byte from the
control register. The following code example shows the use of
viOut8() to update the 1260-145 module.
Summary of Contents for 1260 VXI
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