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SubjectRe: Sounds suspiciously like a homework question :) *nt* Reply to this message
Posted byRiff
Posted on08/10/04 08:21 PM



> > > Assuming the external crystal is set to drive the 6809 @ 8Mhz (which i
> believe
> > > is the top speed the chip can go - on the 68B09), what would the frequency
> of
> > > the E & Q lines be?
> > >
> > > The hardware i'm looking at uses E to pulse a 4020 counter which eventually
> > > toggles the FIRQ of the 6809, and obviously I'm trying to calculate the
> > correct
> > > freq. to generate the firq.
> > >
> > > I've looked over the 6809 datasheet and just don't really follow it. I've
> > never
> > > been good with timing in general, and those datasheets are not written to be
> > > easily understandable unless you already get the concept! :)
> > >
> > > So if someone could explain, not only the answer, but how I could have
> derived
> > > the answer from looking at the datasheet, it would be greatly appreciated..
> > >
> > > Thanks
> > > -Steve
> > >
> >

If you look at Figure 10 - Clock Generator in the Motorola 6809 Technical Data manual, you will notice that E and Q are both nominally half the frequency of the input XTAL frequency. If XTAL is nominally 8 Mhz, E is nominally 4 Mhz. Looking at the clock generator example you should also be aware that it is not always the case that E and Q are always half the frequency of XTAL. In the clock generator circuit, an extra flip-flop is used to generate a signal which adds wait states, causing the duty cycle of E and Q to be stretched out. There may be a limit to how long E and Q can be stretched out. If a 6908B is being used then you don't need to worry about it as the E and Q pins are outputs. The E and Q inputs are meant to provide a means of external synchronization, but I'd have to read through the 6809 manual again to be sure that the internally generated E and Q signal frequencies are constant. If they werent, they probably wouldnt be used for triggering sound generation, so its probably not an issue, allowing for the assumption that they are always clocked at half the frequency of the oscillator input.

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Subject  Posted byPosted On
*E & Q timing on M6809  sellenoff08/09/04 06:15 PM
.*Sounds suspiciously like a homework question :) *nt*  Bart T.08/09/04 11:55 PM
..*Re: Sounds suspiciously like a homework question :) *nt*  sellenoff08/10/04 12:22 PM
...*Re: Sounds suspiciously like a homework question :) *nt*  Bart T.08/10/04 09:12 PM
....*Re: Sounds suspiciously like a homework question :) *nt*  sellenoff08/10/04 11:56 PM
....Re: Sounds suspiciously like a homework question :) *nt*  Riff08/10/04 08:21 PM
....*Re: Sounds suspiciously like a homework question :) *nt*  sellenoff08/10/04 11:53 PM