Re: power on reset prob

Started by Stewart Prince November 20, 2003
In order to overcome any problems with the oscillator not starting up
before the power on reset occurs, we connected a 3406 supervisor IC to
the reset line of a D60a in conjunction with an RC filter of 50 ms to
make sure the oscillator has enough time to oscillate properly. When
using the Tech Arts BDM pod with this system to download our firmware,
communication via BKND was not possible. We probed the BKND line as well
as the RESET and all seemed to work well, but no communication. We then
removed the capacitor from the circuit and everything work well.

My question is: Why might the capacitor and the RC filter, which holds
the RESET line low for 50 ms, interfere with the startup of the
microprocessor, and why would this affect communication between the BDM
pod and our board?

Stewart Prince
Profesor, Mech Eng
CSUN



Stewart,

When programming a target device, programming tools generally reset the
device in Special Single-chip mode. This involves holding the BKGD pin
at Vss during the rising edge of reset. If you have a lot of capacitance
on the Reset line, reset will not rise past its threshold before the
BKGD pin is released. At best the device will come up in Normal single
chip mode & with no code in the target device it will go off into the
weeds. Most likely, however, the BDM tool will attempt to begin BDM
communications before the target device has come out of reset.

Your best bet to produce a delayed reset signal for powerup is to use
one of the Maxim reset circuits containing either a fixed reset delay
(MAX6381 - 6391) or one with a programmable delay (via external capacitor).

Regards,
Gordon

Stewart Prince wrote:

>In order to overcome any problems with the oscillator not starting up
>before the power on reset occurs, we connected a 3406 supervisor IC to
>the reset line of a D60a in conjunction with an RC filter of 50 ms to
>make sure the oscillator has enough time to oscillate properly. When
>using the Tech Arts BDM pod with this system to download our firmware,
>communication via BKND was not possible. We probed the BKND line as well
>as the RESET and all seemed to work well, but no communication. We then
>removed the capacitor from the circuit and everything work well.
>
>My question is: Why might the capacitor and the RC filter, which holds
>the RESET line low for 50 ms, interfere with the startup of the
>microprocessor, and why would this affect communication between the BDM
>pod and our board?
>
>Stewart Prince
>Profesor, Mech Eng
>CSUN >
>-------------------- >
>">http://docs.yahoo.com/info/terms/ >

--
===============================================================
Gordon Doughman Ph: 937-438-6811
Motorola Semiconductor Fax: 937-434-7457
Field Applications Engineer Pager: 800-759-8352 Pin: 1304089
Suite 175
3131 Newmark Drive
Miamisburg, OH 45342

Check out my HC12 book at:
http://www.rtcbooks.com/programming.php



Stewart,

I don't know the specifics of the BDM you use, but in general BDMs need to
control the Reset line of the HC12, as well and the BKGD in order to bring
it up in Special Single Chip mode first.

The recommended Reset connection by Motorola is open-drain. Maybe in your
case the BDM drive Reset as open drain, and rely on the Reset pull-up
resistor to do the un-Reset transition from low to high. When you have the
capacitor installed, the low-to-high transition on the Reset line may be
delayed by the RC, and so if BDM communication starts before Reset was
fully charged to a logic 1, establishing the BDM communication to the HC12
fails.

Hope this helps,
Doron
Nohau Corporation
HC12 In-Circuit Emulators
www.nohau.com/emul12pc.html

At 07:56 20/11/2003 -0800, you wrote:
>In order to overcome any problems with the oscillator not starting up
>before the power on reset occurs, we connected a 3406 supervisor IC to
>the reset line of a D60a in conjunction with an RC filter of 50 ms to
>make sure the oscillator has enough time to oscillate properly. When
>using the Tech Arts BDM pod with this system to download our firmware,
>communication via BKND was not possible. We probed the BKND line as well
>as the RESET and all seemed to work well, but no communication. We then
>removed the capacitor from the circuit and everything work well.
>
>My question is: Why might the capacitor and the RC filter, which holds
>the RESET line low for 50 ms, interfere with the startup of the
>microprocessor, and why would this affect communication between the BDM
>pod and our board?
>
>Stewart Prince
>Profesor, Mech Eng
>CSUN




Stewart Prince <> wrote:

> In order to overcome any problems with the oscillator not starting up
> before the power on reset occurs, we connected a 3406 supervisor IC to
> the reset line of a D60a in conjunction with an RC filter of 50 ms to
> make sure the oscillator has enough time to oscillate properly. When

What do you mean writing "in conjunction with an RC filter": did you
filter the supply of the 34064? This should work. Putting the RC
filter on the Reset line doesn't work, as Gordon wrote.

BTW: I suggest the MAX809-type reset ICs since they are much cheaper
and available from many manufacturers. They have a push-pull output,
but you can use a series resistor between the *809 output and the
/Reset line _instead_ (!) of the usual pullup resistor. This works
fine as long as there are no other pull-up devices connected to the
/Reset line.

Oliver
--
Oliver Betz, Muenchen



> My question is: Why might the capacitor and the RC filter, which
holds
> the RESET line low for 50 ms, interfere with the startup of the
> microprocessor, and why would this affect communication between the
BDM
> pod and our board?

The BDM Pod controls the RESET* line via PT6. Adding RC interferes
with the POD timing when the target comes out of RESET because of
added delay.


--- In , "Oliver Betz" <list_ob@g...> wrote:

> BTW: I suggest the MAX809-type reset ICs since they are much cheaper
> and available from many manufacturers. They have a push-pull output,
> but you can use a series resistor between the *809 output and the
> /Reset line _instead_ (!) of the usual pullup resistor. This works
> fine as long as there are no other pull-up devices connected to the
> /Reset line.


Hi Oliver,

Since you don't know what is inside the BDM pod wouldn't it be prudent to stay with open drain devices and a pull up resistor?
Or do all PODs use open drain?

Any suggestions on voltage level?
Stick with a safe 4.68 V or since these chips seem to be able to run at lower voltages or would you use a tad more margin?

Cheers,

Theo



theobee00 <> wrote:

[I suggest MAX809-type ICs with a series resistor]

> Since you don't know what is inside the BDM pod wouldn't it
> be prudent to stay with open drain devices and a pull up
> resistor?
>
> Or do all PODs use open drain?

IMO, a BDM adapter should not pull the /Reset high unless I select to
do so.

But what happens if the BDM adapter pulls /Reset high? Nothing (I
guess), because usually your supply voltage and oscillator will be
stable in this moment.

> Any suggestions on voltage level?
> Stick with a safe 4.68 V or since these chips seem to be able
> to run at lower voltages or would you use a tad more margin?

Depends on your regulator tolerance and supply decoupling. I use a
4,38V type to allow the use cheap linear regulators (in a HC08
design).

Oliver
--
Oliver Betz, Muenchen



--- In , "Oliver Betz" <list_ob@g...> wrote:
> theobee00 <yahoodump2@o...> wrote:
>
> [I suggest MAX809-type ICs with a series resistor]
>
> > Since you don't know what is inside the BDM pod wouldn't it
> > be prudent to stay with open drain devices and a pull up
> > resistor?
> >
> > Or do all PODs use open drain?
>
> IMO, a BDM adapter should not pull the /Reset high unless I select to
> do so.
>
> But what happens if the BDM adapter pulls /Reset high? Nothing (I
> guess), because usually your supply voltage and oscillator will be
> stable in this moment.

I was more thinking on asserting reset, if the pod also has an ell cheapo Max890 with a series resitor you end up with a 2.5 V reset level asserted from the POD.

Regards,

Theo




theobee00 <> wrote:

[...]

> > But what happens if the BDM adapter pulls /Reset high? Nothing (I
> > guess), because usually your supply voltage and oscillator will be
> > stable in this moment.
>
> I was more thinking on asserting reset, if the pod also has an ell
> cheapo Max890 with a series resitor you end up with a 2.5 V reset
> level asserted from the POD.

The /Reset of the BDM adapter ("pod") CPU shouldn't be connected to
the BDM connector. The /Reset line of the BDM connector has to be
controlled and monitored by the BDM adapter firmware, IOW one or more
port pin(s) of the BDM adapter CPU.

If the BDM adapter has a strong pullup (unexpectedly), and the target
wants to pull down /Reset, well - that's bad luck... (at least until
also the BDM adapter also asserts /Reset). In this case, one can try
to insert a schottky diode in the /Reset connection. Depends on the
volume produced, but likely still cheaper than using expensive reset
chips.

Oliver
--
Oliver Betz, Muenchen



--- In , "Oliver Betz" <list_ob@g...> wrote:
> theobee00 <yahoodump2@o...> wrote:
>
> [...]
>
> > > But what happens if the BDM adapter pulls /Reset high? Nothing (I
> > > guess), because usually your supply voltage and oscillator will be
> > > stable in this moment.
> >
> > I was more thinking on asserting reset, if the pod also has an ell
> > cheapo Max890 with a series resitor you end up with a 2.5 V reset
> > level asserted from the POD.
>
> The /Reset of the BDM adapter ("pod") CPU shouldn't be connected to
> the BDM connector. The /Reset line of the BDM connector has to be
> controlled and monitored by the BDM adapter firmware, IOW one or more
> port pin(s) of the BDM adapter CPU.
>
> If the BDM adapter has a strong pullup (unexpectedly), and the target
> wants to pull down /Reset, well - that's bad luck... (at least until
> also the BDM adapter also asserts /Reset). In this case, one can try
> to insert a schottky diode in the /Reset connection. Depends on the
> volume produced, but likely still cheaper than using expensive reset
> chips.

Hi Oliver, you convinced me, el cheapo here we come.

Now see if we can get them here.

Cheers,

Theo