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SCC68070

The SCC68070 is a discontinued Motorola 68000–based 16/32-bit processor produced under license by Philips Semiconductors. The processor was co-developed by Philips Semiconductors and Signetics and introduced in October 1985.[1] Philips had been a second source of the Motorola 68000 before introducing the 68070.[2] It was marketed by Philips as a high-performance microcontroller to compete with the Intel 80186. It suffered from poor adoption rates on account of its high cost due to the large size of its die.[3] In 1990, Philips released the companion SCC66470 VSC (Video and Systems Controller) for the 68070.[4] Both were adopted for Philips‘s ill-fated CD-i line of interactive entertainment systems.[5] The CD-i soon became the 68070’s overwhelming usage.[6]: 33 

Specifications

The Philips 68070 was initially fabricated with a 2-μm CMOS process and was packaged in an 84-pin plastic leaded chip carrier.[7] Additions to the Motorola 68000 core include:

  • Operation from 4 to 17.5 MHz[6]: 33 
  • Inclusion of a minimal, segmented MMU supporting up to 16 MB of memory[8]
  • Built-in DMA controller[9]
  • I2C bus controller[9]
  • UART[8]
  • 16-bit counter/timer unit[10]
  • 2 match/count/capture registers allowing the implementation of a pulse generator, event counter or reference timer[11]
  • Clock generator[7]

Differences from the Motorola 68000 core include the following:

  • Instruction execution timing is completely different.[6]
  • Interrupt handling has been simplified.
  • The SCC68070 has MC68010 style bus-error recovery. They are not compatible, so exception error processing is different.
  • The SCC68070 lacks a dedicated address generation unit (AGU), so operations requiring address calculation run slower due to contention with the shared ALU. This means that most instructions take more cycles to execute, for some instructions significantly more, than a 68000.
  • The MMU is not compatible with the Motorola 68451 or any other “standard” Motorola MMU, so operating system code dealing with memory protection and address translation is not generally portable. Enabling the MMU also costs a wait state on each memory access.

While the SCC68070 is mostly binary compatible with the Motorola 68000,[11] there is no equivalent chip in the Motorola 680×0 series. In particular, the SCC68070 is not a follow-up to the Motorola 68060, which came out in 1994 (postdating the 68070 by nearly a decade).[6]: 33 

References

  1. ^ Bursky, Dave (October 31, 1985). “CMOS µP runs 68000 code, carries its own MMU”. Electronic Design. Vol. 33, no. 25. Endeavor Business Media. p. 46 – via Google Books.
  2. ^ Bernhard, Robert (June 19, 1986). “Veteran 16-bit Microprocessors Still Battling for Designers’ Favor”. Electronic Design. Vol. 34. Endeavor Business Media. pp. 27 et seq. – via Gale.
  3. ^ “Microprocessors for Embedded Control”. Understanding RISC Microprocessors: 140 Articles Originally Published in Microprocessor Report Between March 1988 and November 1992. Microprocessor Report. 1992 [February 7, 1990]. p. 1.15 – via Google Books.
  4. ^ Torofex, John (June 9, 1990). “Your Format: QL”. New Computer Express. No. 83. Future Publishing. p. 11 – via the Internet Archive.
  5. ^ Pitre, Boisy G.; Bill Loguidice (2013). CoCo: The Colorful History of Tandy’s Underdog Computer. CRC Press. p. 145. ISBN 1040071597 – via Google Books.
  6. ^ a b c d Goodwin, Simon (August 1995). “Chips with everything”. Amiga Format. No. 74. Future Publishing. pp. 31–33 – via the Internet Archive.
  7. ^ a b Erikson, Arthur, ed. (October 28, 1985). “Philips, Signetics to Bring Out Enhanced 68000-Compatible CPU”. Electronics. Vol. 58, no. 43. McGraw-Hill. p. 63 – via Google Books.
  8. ^ a b Mokhoff, Nicolas (November 15, 1985). “Alternate sources combine 68000, MMU, and more, on one chip”. Computer Design. Vol. 24, no. 16. PennWell Publishing. pp. 23–24. Gale A661987 – via Google Books.
  9. ^ a b Staff writers (December 29, 1986). “The Best of 1986”. Electronic Design. Vol. 34. Endeavor Business Media. pp. 36–141 – via Google Books.
  10. ^ Staff writer (January 1986). “Philips bring DMA/MMU within 68000 IC”. Electronic Engineering. Vol. 58. Morgan-Grampian. p. 17 – via Google Books.
  11. ^ a b Clements, Alan (1990). 68000 Sourcebook. McGraw-Hill. pp. 340–341. ISBN 0070113211 – via Google Books.