Forums

ESSI Clock and Chip Select

Started by hardeepgida March 15, 2005

Hi,

I am a "newbie" using the ESSI on the DSP56858(programmed by
Codewarrior + Processor Expert). In the manual it says that the
serial clock on the ESSI is continous (which i'm assuming means that
it is on at all times). However, what I would like it to do is the
following: When chip select is high, the clock should be off. When
chip select is low, the clock should turn on. Is there a register
that controls this continuous/non-continous functionality of the
clock? Is there a way that I can somehow programmably AND the Chip
select signal and serial Clock signal so that I can turn the clock
on and off? Would I have to use a hardware AND gate?

Thank you.
Hardeep




I contacted freescale and they provided me with the following
response (This may help others who are trying to figure out
continuos/gated clock modes. The reason why this is confusing is
because in the pin descriptions chapter of the manual, freescale
mentions that continuous and gated clocks are possible, but in the
ESSI chapter, it does not mention anything about the gated clocks
option):

The ESSI peripheral will only generate a continuous clock. By gated
clock, it means that the peripheral internal hardware will ignore
bit clocks that occur on a clock input when they are outside of a
valid frame. Some external devices require a gated clock to operate
and if they cannot generate the gated clock themselves, external
logic will be needed if the DSP is to generate it.

Thanks.
Hardeep --- In , "hardeepgida" <hgida@i...> wrote:
>
> Hi,
>
> I am a "newbie" using the ESSI on the DSP56858(programmed by
> Codewarrior + Processor Expert). In the manual it says that the
> serial clock on the ESSI is continous (which i'm assuming means
that
> it is on at all times). However, what I would like it to do is the
> following: When chip select is high, the clock should be off. When
> chip select is low, the clock should turn on. Is there a register
> that controls this continuous/non-continous functionality of the
> clock? Is there a way that I can somehow programmably AND the Chip
> select signal and serial Clock signal so that I can turn the clock
> on and off? Would I have to use a hardware AND gate?
>
> Thank you.
> Hardeep



Hardeep,

I believe what the manual is trying to say is that the ESSI will accept
a gated clock input generated by an external device. Meaning the ESSI
does not require a continuous clock to operate properly. However, the
ESSI hardware is not capable of generating a gated clock output. At
least this is the case for the 56300 Family which I believe is
extremely similar with repsect to ESSI operation.

--
dB --- hardeepgida <> wrote:
>
> I contacted freescale and they provided me with the following
> response (This may help others who are trying to figure out
> continuos/gated clock modes. The reason why this is confusing is
> because in the pin descriptions chapter of the manual, freescale
> mentions that continuous and gated clocks are possible, but in the
> ESSI chapter, it does not mention anything about the gated clocks
> option):
>
> The ESSI peripheral will only generate a continuous clock. By gated
> clock, it means that the peripheral internal hardware will ignore
> bit clocks that occur on a clock input when they are outside of a
> valid frame. Some external devices require a gated clock to operate
> and if they cannot generate the gated clock themselves, external
> logic will be needed if the DSP is to generate it.
>
> Thanks.
> Hardeep > --- In , "hardeepgida" <hgida@i...> wrote:
> >
> > Hi,
> >
> > I am a "newbie" using the ESSI on the DSP56858(programmed by
> > Codewarrior + Processor Expert). In the manual it says that the
> > serial clock on the ESSI is continous (which i'm assuming means
> that
> > it is on at all times). However, what I would like it to do is the
> > following: When chip select is high, the clock should be off. When
> > chip select is low, the clock should turn on. Is there a register
> > that controls this continuous/non-continous functionality of the
> > clock? Is there a way that I can somehow programmably AND the Chip
> > select signal and serial Clock signal so that I can turn the clock
> > on and off? Would I have to use a hardware AND gate?
> >
> > Thank you.
> > Hardeep >
>
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