Re: reset cycle for 6800

jchausler wrote:

Chris Croughton wrote:



On 28 Mar 2006 06:36:29 -0800, A68
<asmara_lebanon@xxxxxxxxxxxx> wrote:



3.
What is the requirement for providing "phase 1" and "phase 2" if I
don't have the proper clock chip such as 6875.


See the specification. As I recall it's a little more complex than just
using an inverter because of the non-overlapping rule (the two clocks
mustn't both be high at the same time). The MC6875 datasheet has an
equivalent circuit (from which you could build in discrete TTL, but most
of it is used to do the memory hold-off for slow memory (lengthening the
phase until the memory is ready) and DMA, the basic circuit for constant
running is just a D-type flip-flop with feedback (!Q to D) and the two
phases being from Q and !Q.

The datasheet can be obtained from:
http://www.datasheetcatalog.com/datasheets_pdf/M/C/6/8/MC6875.shtml)



IIRC the Motorola D1 kit used a dual one shot (8602?) but a funny.
MC3459 IIRC, chip to drive the inputs to the processor due to some
kind of loading problem. I doubt 3459's are available any more.


As I remember the 6800 required clock voltage that was a little higher ( or lower ) than TTL
could provide.That was in addition to the timing constraints



4.
How does 6800 store text file to floppy disk.


With a disk driver. Sorry, I don't have code for one (and it would
depend on the interface to the floppy and what file system you want to
use as well). But that is a lot higher level.



There were several floppy operating systems for the 6800.
I used FLEX and there is a FLEX USERS GROUP on the net,
it was the most popular and there are versions for various hardware
configurations. Mine uses the popular 1771 floppy controller for
5 1/4 inch floppies in a PIO mode. The 6800 was not fast enough
to read 8 inch floppies in PIO mode so a DMA controller was
required. The 6809 could handle both in PIO mode. There were
versions of FLEX for both the 6800 and the 6809. There is still
a lot of activity in this area.



I think the 2 MHz version (B) of the 6800 was fast enough for the 8 inch or 3 1/2 inch drives

Midwest Scientific Instruments had MSI DOS is another one
out there with some continuing interest. Percom had a very
basic floppy disk system. I never used it but IIRC you had
to keep your own disk catalog.

Regards,
Chris




You should get on the FUG mailing list. There is an active (small) group, many of
them were active in designing software and hardware for the Motorola chips.

Bill K7NOM

Relevant Pages

  • Re: Patch: Make iBook1 work again
    ... > backlight can be either done by the ATI chip or by some other uController ... their clock is removed but not their power. ... Luckily the BIOS on my Rage LT Pro did use SCLK to clock the engine, ...
    (Linux-Kernel)
  • Re: Virtex 4, LVDS I/O: Sanity check please
    ... The buses theoretically could use a single clock and a single framing signal ... for a total of 150 pins total and the same on the opposite side of the chip. ... If I have to use resistors, ... I would like the number of bus connections between chips in any ...
    (comp.arch.fpga)
  • Re: WTD: WWVB receiver
    ... it could be a corner of a chip. ... But now I don't have to wait for a Digikey order if I quickly need to pipe out some alphanumeric data. ... Looks like buying an atomic clock at Walmart and parting it out is going to cost less. ...
    (sci.electronics.design)
  • [PATCH][RFT] HPT3xx: init code rewrite
    ... on 66 MHz PCI) caused by the HighPoint's ... habit of switching the base DPLL clock with every new revision of the chips... ... switch to using the enumeration type to differ between the numerous chip ... stop duplicating it for each channel by storing the pointer in the pci_dev ...
    (Linux-Kernel)
  • Re: strange serial-to-parallel shift-register chip
    ... > chip, TI's sn74lv8153. ... > with no clock line. ... > Two consecutive serial-data frames transmit 8 bits of data. ... Looks suspiciously like LIN, ...
    (sci.electronics.design)