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Chapter 3
Technical Information
This chapter contains detailed information for advanced users who
want to increase the power of the GPIB-SCSI-A.
The GPIB-SCSI-A is actually a powerful 8-bit microcomputer tailored for
use as an IEEE 488-to-SCSI protocol controller. The operating system of
the unit is contained in Read-Only Memory (ROM) and 256 kilobytes of
Dynamic Random-Access Memory (DRAM). The GPIB-SCSI-A
microprocessor operates at 10 MHz and contains an integrated Direct
Memory Access (DMA) controller for high-speed data transfers from the
GPIB and SCSI circuitry. The processor also contains an integrated
memory management unit, a DRAM refresh controller, a clock generator, a
programmable timer unit, and an interrupt controller.
All GPIB functionality is provided by a NAT4882 application-specific
integrated circuit (ASIC) GPIB Controller chip, which is programmed and
maintained by the operating system. All SCSI functionality is provided by
an LSI SCSI controller chip, which is also programmed and maintained by
the operating system. Both the GPIB and SCSI ports use interrupt
conditions to process important events on either bus. The remainder of this
chapter contains additional technical information for each mode of
operation.
Note:
Unless stated otherwise, all numbers presented in this chapter are
in decimal notation.
Assumption of Previous Knowledge
This chapter assumes that you have a basic knowledge of the SCSI bus. If
you are a first-time user or you would like to review the basics, refer to
Appendix D, Operation of the SCSI, for a history of and a basic introduction
to the SCSI.
© National Instruments Corp.
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GPIB-SCSI-A User Manual