RS-422 interface for SBus

The SCD-20 is a discontinued product, and is no longer supported. This information is is provided for reference only.

  • Transfer rates up to 20 MB per second.
  • 1 KByte FIFO
  • Implements a high speed DMA channel between an external device and Sun SPARCstation
  • RS-422 compatible driver/receivers
  • Customizable by a RAM-based programmable gate array
  • Synchronous protocol
  • Clock timing from DMA interface, user device or both
  • Sun SPARCstation compatible
  • Device drivers for Solaris 1.x (SunOS 4.1.x) and Solaris 2.6+ (SunOS 5.x)
  • Single SBus slot

The SCD-20 interface provides a high speed 16-bit parallel DMA channel between an external device and a Sun SPARCstation. The device interface uses RS422 compatible driver/receivers connected to a RAM based programmable gate array and 1 KByte FlFOs. The SCD-20 uses Direct Virtual Memory Access (DVMA) and asynchronous I/O to achieve transfer rates to or from memory of up to 20 MB per second. The hardware protocol is synchronous. That is, all data and control signals are sampled with a clock transmitted along with the data and control signals. This clock may be generated by the DMA interface or the user device or both. All signals are differential using RS422 specifications. The SCD-20 includes a versatile, straightforward protocol but optional customer-specific protocols may be developed.

  • Imaging devices
  • Scanners
  • Plotters
  • Research and development

A standard SunOS loadable device driver for the SPARCstation is included with the SCD-20. The driver provides access to the SCD-20 through standard and asynchronous read and write system calls. Continuous transfers are implemented with asynchronous I/O.

The SCD-20 is provided with minimal Codes PROM for identification only. User Code PROMS MAY be developed for specific applications.


EDT provides several levels of customer support, from phone consultation to custom design of hardware, software, or FCode drivers, at hourly rates. Technical support is also provided though the Technical Support section of this web site.


SBus compliance

DVMA master
1, 2, 4, 8, or, 16 words per transfer – the largest accommodated by the host computer
25 Mhz maximum clock
Level 5 interrupt
SBus memory space approximately 66K bytes

Device interface


Synchronous streaming


1 KB FIFO for input 1 KB FIFO for output


AMP 787190-8 high-density 80-pin (mates with AMP 749621-8, backshell 749196-2)
high density 80 pin


Temperature: Operating, 10° to 40° C; non-operating, -20° to 60° C

Humidity: Operating, 20% to 80% noncondensing at 40° C; non-operating, 95% noncondensing at 40° C


Single standard SBus slot
Dimensions: 3.3″ x 5.78″ x 0.5″
Weight: 3.5 oz.


1.2A at 5 volts


Software drivers for Solaris 1.x (SunOS 4.1.x) and Solaris 2.x (SunOS 5.x)
Standard read/write system call support
Asynchronous I/O support for continuous transfers