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DTACK Grounded

January 01, 1970

DTACK Grounded was a computer hobbyist newsletter published from July 1981 to September 1985 by Hal W. Hardenberg.[1] Subtitled "The Journal of Simple 68000 Systems", the newsletter was dedicated to the proposition that the Motorola 68000 CPU could be used to build simple, fast computers. In 1981 this was a revolutionary idea. This was before 68000-based personal computers like the Sharp X68000, Macintosh, Amiga, and Atari ST had been created. In 1981 Motorola was marketing the 68000 solely as a CPU for Unix workstations. Hal believed that the 68000 could be used as a simple embedded microprocessor as well, and used the newsletter to explain how to do that.

Editor Hal W. Hardenberg edit

Hal was the editor of the newsletter and wrote almost all of its content. The ostensible purpose of the newsletter was to promote Hal's company's line of 68000-based hardware and software. However, Hal never let that get in the way of telling a good story or explaining how to design or build a fast computer. He was a hardware engineer and a businessman who also knew how to write software. His newsletter was full of amusing and educational stories about the way the personal computer hardware business worked, and strong opinions about the best way to design personal computer hardware and software.[2]

Etymology edit

"DTACK" is the name of a pin on the Motorola 68000 CPU that informs the CPU that data is ready to be read from memory. It stands for "Data Transfer Acknowledge."[3]

If a system has fast enough memory, this pin can be connected directly to the ground plane (or "grounded") to produce the fastest-possible memory read/write time.[4] However, any complex system would almost certainly have several different types of devices (RAM, ROM, various peripherals) that would support different speeds of access, which in a large system would normally be accommodated by using the DTACK line to insert "wait states"—delays—into bus cycles. (The 68000 has no separate I/O address space, so all I/O devices must be memory-mapped.) The logic circuitry required to pulse DTACK high to add these delays could be fairly complex. Therefore, typically only relatively simple systems can use a design with "DTACK grounded" (i.e., DTACK always asserted). When many different peripherals with different maximum speed capabilities must be used in a small system, another solution to keep DTACK grounded is to slow down the clock rate of the CPU so that all memory and peripheral devices can transfer data at the (reduced) maximum speed of the CPU. In turn, using a lower CPU clock frequency enables a simpler, less expensive circuit board design, with fewer layers, to be used successfully. This, too, like limiting the system to a few peripherals of low diversity, is a design strategy that is typically applied to small or embedded systems but would not be appropriate for high-performance workstations.

Many other microprocessors, including the Intel 8086, 8088, 80286, 80386, 8080, 8085, Zilog Z80, and 6502 family, each have an input pin that serves a similar function to DTACK, but it is usually named READY or RDY. (On the Z80, it is named WAIT.) Therefore, a reference to DTACK distinctively implies the 68000 family of CPUs.

The Redlands edit

In order to discourage photocopying of the newsletter, a portion of the DTACK Grounded newsletter was printed on dark red paper. This made it harder to photocopy those pages. This section of the newsletter was called "the Redlands". It typically contained the assembly source code for high performance math subroutines.

DBASIC edit

A major topic in later years of the newsletter was the Halgol interpreter, later converted to the DBASIC interpreter. Hal produced a fast Basic interpreter for the Atari ST computer. It was written in hand-tuned assembly language, and ran very fast compared to other Basics. But it was non-standard: it couldn't run Microsoft BASIC programs, and it couldn't read or write MS-DOS format floppy disks. Unfortunately, as a result, it was not very popular.[5][6]

Legacy edit

In the 1990s, Hal revived DTACK Grounded as an occasional column in Dr. Dobb's Journal called "DTACK Revisited".[7]

References edit

  1. ^ "DTACK GROUNDED Archive". www.easy68k.com.
  2. ^ "Hal W. Hardenbergh (Felger Carbon) died - RIP - SPCR". silentpcreview.com.
  3. ^ "68000 User's Manual" (PDF). nxp.com. Retrieved 2021-09-27.
  4. ^ http://www.dadhacker.com/blog/?p=1064 Description of DTACK Grounded from an Atari ST Operating System engineer
  5. ^ "DTACK GROUNDED -- DBASIC Post Mortem". www.easy68k.com.
  6. ^ "A New BASIC for the ST -- Or Is It The ST?" p. 9. "Compute!'s Atari ST". December 1987.
  7. ^ Hardenberg, Hal W. "DTACK Revisited". Dr. Dobb's.

January 01, 1970
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This article may need to be rewritten to comply with Wikipedia s quality standards You can help The talk page may contain suggestions September 2020 DTACK Grounded was a computer hobbyist newsletter published from July 1981 to September 1985 by Hal W Hardenberg 1 Subtitled The Journal of Simple 68000 Systems the newsletter was dedicated to the proposition that the Motorola 68000 CPU could be used to build simple fast computers In 1981 this was a revolutionary idea This was before 68000 based personal computers like the Sharp X68000 Macintosh Amiga and Atari ST had been created In 1981 Motorola was marketing the 68000 solely as a CPU for Unix workstations Hal believed that the 68000 could be used as a simple embedded microprocessor as well and used the newsletter to explain how to do that Contents 1 Editor Hal W Hardenberg 2 Etymology 3 The Redlands 4 DBASIC 5 Legacy 6 ReferencesEditor Hal W Hardenberg editHal was the editor of the newsletter and wrote almost all of its content The ostensible purpose of the newsletter was to promote Hal s company s line of 68000 based hardware and software However Hal never let that get in the way of telling a good story or explaining how to design or build a fast computer He was a hardware engineer and a businessman who also knew how to write software His newsletter was full of amusing and educational stories about the way the personal computer hardware business worked and strong opinions about the best way to design personal computer hardware and software 2 Etymology edit DTACK is the name of a pin on the Motorola 68000 CPU that informs the CPU that data is ready to be read from memory It stands for Data Transfer Acknowledge 3 If a system has fast enough memory this pin can be connected directly to the ground plane or grounded to produce the fastest possible memory read write time 4 However any complex system would almost certainly have several different types of devices RAM ROM various peripherals that would support different speeds of access which in a large system would normally be accommodated by using the DTACK line to insert wait states delays into bus cycles The 68000 has no separate I O address space so all I O devices must be memory mapped The logic circuitry required to pulse DTACK high to add these delays could be fairly complex Therefore typically only relatively simple systems can use a design with DTACK grounded i e DTACK always asserted When many different peripherals with different maximum speed capabilities must be used in a small system another solution to keep DTACK grounded is to slow down the clock rate of the CPU so that all memory and peripheral devices can transfer data at the reduced maximum speed of the CPU In turn using a lower CPU clock frequency enables a simpler less expensive circuit board design with fewer layers to be used successfully This too like limiting the system to a few peripherals of low diversity is a design strategy that is typically applied to small or embedded systems but would not be appropriate for high performance workstations Many other microprocessors including the Intel 8086 8088 80286 80386 8080 8085 Zilog Z80 and 6502 family each have an input pin that serves a similar function to DTACK but it is usually named READY or RDY On the Z80 it is named WAIT Therefore a reference to DTACK distinctively implies the 68000 family of CPUs The Redlands editIn order to discourage photocopying of the newsletter a portion of the DTACK Grounded newsletter was printed on dark red paper This made it harder to photocopy those pages This section of the newsletter was called the Redlands It typically contained the assembly source code for high performance math subroutines DBASIC editA major topic in later years of the newsletter was the Halgol interpreter later converted to the DBASIC interpreter Hal produced a fast Basic interpreter for the Atari ST computer It was written in hand tuned assembly language and ran very fast compared to other Basics But it was non standard it couldn t run Microsoft BASIC programs and it couldn t read or write MS DOS format floppy disks Unfortunately as a result it was not very popular 5 6 Legacy editIn the 1990s Hal revived DTACK Grounded as an occasional column in Dr Dobb s Journal called DTACK Revisited 7 References edit DTACK GROUNDED Archive www easy68k com Hal W Hardenbergh Felger Carbon died RIP SPCR silentpcreview com 68000 User s Manual PDF nxp com Retrieved 2021 09 27 http www dadhacker com blog p 1064 Description of DTACK Grounded from an Atari ST Operating System engineer DTACK GROUNDED DBASIC Post Mortem www easy68k com A New BASIC for the ST Or Is It The ST p 9 Compute s Atari ST December 1987 Hardenberg Hal W DTACK Revisited Dr Dobb s Retrieved from https en wikipedia org w index php title DTACK Grounded amp oldid 1217397155, wikipedia, wiki, book, books, library,

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