The xSht register class is used for reading and writing bit fields of simple digital registers within the short I/O address space of VXI cards. Access to the hardware must involve only a single access via the VXI backplane.

Whole words can be accessed by setting the length and bit attributes to zero.
The class accepts values in decimal or hex format.

All address variables are VME addresses and are thus expressed in units of bytes (8 bits).

Attributes :-

-s    VXI slot number

specifies the slot number (1-12) within the VXI crate. Manditory - no default value.

-o    offset

specifies the address offset of the hardware register relative to the base address of the VXI card allocated by the Resource Manager. Manditory - no default value.

-w    width of VME access. Options are 8; 16; 32.

specifies the data width required for accesses to the VXI hardware register.

-p    access permission (rw, ro, wo)

specifies the data access modes permitted to the VXI hardware register. Options are ro (read only); wo (write only); rw (read-write).

-l    length of bit field

specifies the length of the data field for this register in bits.
The server code permits access to VXI hardware registers at the bit level. The hardware will always be accessed using the access width specified by the -w attribute. The server however implements in software objects which may be any subfield of a hardware register. For write access to a subfield of a hardware register it is required that the hardware be readable.
The attribute value -l 0 implies that the data field for this object is the same as the hardware access width specified by the -w attribute. Optional. By default -l 0 is assumed.

-b    bit position

specifies the position of the least significant bit of the data within the hardware register. The hardware is addressed with the least significant bit having the value 0.
This attribute will normally always be used in conjunction with the -l attribute to define the length and position of a software object which is a subfield of the hardware register. Optional. By default -b 0 is assumed.

-f    data format

specifies the data format to be used by READ operations. Data can be return in decimal (d) or hexadecimal (x). The default is hexadecimal.

-i    initial value

specifies the data value to be used by the INITIALISE operation. The register must also have write permission.