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1260-21 User Manual
Racal Instruments
©
2005
Module Operation 3-5
The Read Back status reads the coil value for each relay inverted.
When the relay coil is deactivated by setting the relay control bit to
‘0’ (switch is in the Normally Closed position) the Read Back bit is
‘1’. When the relay coil is activated by setting the relay control bit
to ‘1’ (switch is in the Normally Open position) the Read Back bit is
‘0’.
The control registers are located in the VXI bus A24 Address
Space. The A24 address for a control register depends on:
1. The A24 Address Offset assigned to the 1260-01T module by
the Resource Manager program. The Resource Manager
program is provided by the VXI bus slot-0 controller vendor.
The A24 Address Offset is placed into the “Offset Register” of
the 1260-01T by the Resource Manager.
2. The <module address> of the 1260-21 module. This is a
value in the range 1 through 12.
3. Each control register/status register on the 1260-21 has a
unique address.
The base A24 address for the 1260-21 module may be calculated
by:
(A24 Offset of Option-01T) + (1024 x Module Address of
1260-21).
The A24 address offset is usually expressed in hexadecimal. A
typical value of 204000
16
is used in the examples that follow.
A 1260-21 with a module address of 6 would have the base A24
address computed as follows:
Base A24 Address of 1260-21 = 204000
16
+ (400
16
x 6
10
)
=
205800
16
The control registers for 1260-Series VXI modules are always on
odd-numbered A24 addresses. The two control registers for the
1260-21 reside at the first two odd-numbered A24 addresses for
the module:
(Base A24 Address of 1260-21) + 1 = Control Reg. 0
(Base A24 Address of 1260-21) + 3 = Control Reg. 1