DP256 : oscillateur

Started by February 28, 2003

Hi Guillermo

Do you have a schematic of this?
Do you use a 16MHz oscillator or quartz which type of system (P or C) is
better?

We cannot go higher than 36MHz with a first evaluation board DP256 from
Motorola !!!

Best regards
Jean-Pierre "Guillermo F. Molina" <> le 28/02/2003 01:10:40

Veuillez rondre

Pour :
cc : (ccc : Jean-Pierre CEYSSON/Valence)

Objet : Re: [68HC12] Problem of reset with 9S12DG256




Jean-Pierre,

As far as I know the DP256 cannot work with Pierce crystal configuration.
It can only work with Colpitts or external 2.5V square wave clock.

The MC9S12Dx128 and MC9S12Dx64, and newer HCS12 parts can also work with
the Pierce crystal configuration (in addition to the Colpitts and the
external 2.5V square wave clock).

The Colpitts crystal configuration is specified for up to 16MHz. It has
reduced voltage swing which is designed to reduce the oscillator circuit
power consumption, but also makes it more susceptible to noise. You should
pay close attention to leakage current in this crystal configuration. Some
people on the list have offered in the past to coat the Colpitts crystal
components to prevent leakage current. Some crystals also require a DC
blocking capacitor to work properly and to prevent long term degradation of
the crystal circuit due to the DC voltage that is otherwise applied to the
crystal.

The Pierce crystal configuration can work to frequencies of 40MHz. It is
more power hungry than the Colpitts crystal configuration, but less
susceptible to noise due to the increased 2.5V voltage swing. In order to
use this configuration, PE7 should be pulled down during Reset. This
configuration is more forgiving than the Colpitts, and should be considered
if you are not very concerned about power consumption.

An external 2.5V square wave clock from a clock oscillator can work to
50MHz. However as pointed out by Guillermo, the specified rise time and
fall time as well as the 50% duty cycle are very hard to meet at 50MHz.
Then on the other hand, this configuration is working on the Nohau
emulators that I design to 66MHz in room temperature. So if you don't
expect your board to work at extreme temperatures (-55 to 125 Celsius), it
may work just fine at 50MHz, at less strict rise/fall and duty-cycle
requirements.

A common configuration that many people are using with the DP256 is a 4MHz
Colpitts crystal, and the use the internal PLL to bump up the internal
speed to 48MHz or 50MHz (24MHz or 25MHz bus speed).

Hope this helps,

Doron
Nohau Corporation
HC12 In-Circuit Emulators
www.nohau.com/emul12pc.html At 08:52 AM 2/28/2003 +0100, you wrote:

>Hi Guillermo
>
>Do you have a schematic of this?
>Do you use a 16MHz oscillator or quartz which type of system (P or C) is
>better?
>
>We cannot go higher than 36MHz with a first evaluation board DP256 from
>Motorola !!!
>
>Best regards
>Jean-Pierre >"Guillermo F. Molina" <> le 28/02/2003 01:10:40
>
>Veuillez rondre
>
>Pour :
>cc : (ccc : Jean-Pierre CEYSSON/Valence)
>
>Objet : Re: [68HC12] Problem of reset with 9S12DG256



Hi Jean-Pierre,
I'm using a ECS-2200B canned 16 Mhz oscillator. This was my choice because I
want to be sure that I don't have crystal, startup or noise problems and I
can afford the extra cost of the canned osc in this design.
I think that using a 4 Mhz cristal and the PLL (as Doron Fael suggests) is a
good (and cheaper) choice too.
Regards,
Guillermo.

----- Original Message -----
From: <>
To: <>
Sent: Friday, February 28, 2003 4:52 AM
Subject: [68HC12] DP256 : oscillateur >
> Hi Guillermo
>
> Do you have a schematic of this?
> Do you use a 16MHz oscillator or quartz which type of system (P or C) is
> better?
>
> We cannot go higher than 36MHz with a first evaluation board DP256 from
> Motorola !!!
>
> Best regards
> Jean-Pierre > "Guillermo F. Molina" <> le 28/02/2003 01:10:40
>
> Veuillez rondre
>
> Pour :
> cc : (ccc : Jean-Pierre CEYSSON/Valence)
>
> Objet : Re: [68HC12] Problem of reset with 9S12DG256 > -------------------- >
> ">http://docs.yahoo.com/info/terms/




Doron Fael wrote:

[Colpitts oscillator]

> noise. You should pay close attention to leakage current in this
> crystal configuration. Some people on the list have offered in the

To my experience, tens of uA don't hurt, so only in a _very_ harsh
environment one should care about leakage currents.

Noise is especially a problem if the PLL is not used.

Oliver
--
Oliver Betz, Muenchen