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Register-Based Programming 87Appendix B
Appendix B
Register-Based Programming
About This Appendix
This appendix contains the information you can use for register-based
programming of the E1442A. The contents include:
• Register Programming vs. SCPI Programming . . . . . . . . . . . .85
• Addressing the Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . .85
• Register-Based Programming the E1442A. . . . . . . . . . . . . . . .88
• Register Definitions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .92
• Programming Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .94
Register Programming vs. SCPI Programming
The E1442A 64-Channel Form C Switch Module is a register-based module
that does not support the VXIbus word serial protocol. When a SCPI
command is sent to the Form C switch, the E1406 Command Module parses
the command and programs the switch at the register level.
NOTE If SCPI is used to control this module, register programming is not
recommended. The SCPI driver maintains an image of the card state.
The driver will be unaware of changes to the card state if you alter the
card state by using register writes.
Register-based programming is a series of reads and writes directly to the
Form C switch registers. This increases throughput speed since it
eliminates command parsing and allows the use of an embedded controller.
Also, if slot 0, the resource manager, and the computer GPIB interface are
provided by other devices, a C-size system can be downsized by removing
the command module.
Addressing the Registers
Register addresses for register-based devices are located in the upper 25%
of VXI A16 address space. Every VXI device (up to 256 devices) is allocated
a 32-word (64-byte) block of addresses. With seven registers, the E1442A
Form C Switch Module uses seven of the 64 addresses allocated.