problem with active clock source (DS1077L) / ISP Voltage

simon

Hi!

I am using a DS1077L Econ Oscillator from Maxim-IC.com as the main clock source.
My whole circuit is running at 3V and the Oscillator should be connected to OSC1.

Now the Problem:
I need to do in-circuit programming.
As far as i know the Programmer applies 12V to OSC1 during
the writing phase which might damage the Osc.

How could i solve this ?
I can not add a jumper at position "?" (see attached pic) to physically disconnect the osc. during ISP.

I thought about these Solutions:
1) use a diode, problem: will this work for a 50-75 Mhz clock ?
2) use a 5kOhm resistor, the osc kann source/sink +-4mA -> I = 12V / 5000 = 2.4mA
problem: i am not sure what happens to the osc if he gets 12V instead of 5v

I already wrote maxim about that but i do not expect an answer.

Another question: will the running clock do some bad things while using the ISP ?

Bye, Simon

Peter Verkaik

As far as I know, you MUST disconnect any active clock

circuitry to program/debug an SX chip.

Or disconnect that clock completely from the SX

and put in a resonator. This can be left in place

while programming. For debugging I am not sure.

regards peter

Stephen

A diode in series from the clock output doesn't work either... The oscllators are CMOS devices, and as such typically spec an absolute max on the output pin of 7V.

PJMonty

Simon,

I use TTL oscillators, and my experience with them is that it's a jumper or no in circuit progrmming.

Thanks, PeterM

Guenther Daubach

Simon,

In one applicationI used another clock generator chip, and even though it had an option to turn off the clock output to high-Z, it messed up the programming process (and debugging as well). Therefore, I think adding the jumper is the best solution.

BTW: Your schematic shows a 5-pin header for the ISP connection - this looks a bit "exotic", and does not match the SX-Key .

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Greetings from Germany,


G

simon

Hi!

@Peter:
Are you sure ? The ISP programming part says that when using an external
clock source the osc1 pin is driven low during isp in order to stop the ext. clock source.
I remember that i read somewhere something like
"if your clock source can deal with a voltage of 12V on its output you might left it in place"
But i am not sure where i read taht *g*

@Stephen:
If i connect it this way:
[noparse][[/noparse]Oscilator]

---

[noparse][[/noparse]>|---+--[noparse][[/noparse]SX]
and my ISP is connected to + the OScillator is not connected to 12V.
But the Problem is that this solution produces a short circuit (if OSC=3V and ISP=GND).

@Peter:
that does not sound very good [noparse]:([/noparse]

@Guenter:
Jes, i do not use the sx-key 8)
I am using a homebuilt programming adapter with uses a pic16F84 to program the sx [noparse];)[/noparse]
(google for dlscenix, i modified it to support the sx52).
The 5pin connector has the following reason:
you cant connect it in the wrong way
One pin is removed and the connector is modified so it cant fit in the other way 8)
But this connector will be removed later and replaced by some
solder points on the circuit.
The whole system has to be as small as possible.
It is going to be a vision system for our small soccer playing robot
(university project, see: http://robosoccer.de/Roboterfussball.278.0.html?&L=1).

I think i will try to put a 5kOhm resistor in series and try it with my prototype board.
The Econ Oscillators seem to be very robust, i am accidently running a 3V Oscillator
on my prototype board at 5V withour any problems yet.
(during isp i disconnect the osc, but this is only practicable on my prototype board [noparse]:([/noparse] )

Bye, Simon

Guenther Daubach

Simon,

good idea to index the ISP headers to avoid connecting the programmer the wrong way.

On the other hand, my experiences with the SX-Key and the SX itself are that they seem to be quite "dummy-proof". I connected the SX-Key the wrong way more than once, and I also inserted the SX the wrong way in its socket several times. In all cases the devices "stayed alive" .

OK, try the 5kOhm resistor, this may protect the Econ Oscillator. I know that you do your app using the SXC compiler, so you don't debug the code with SX-Key, which might require the jumper.

BTW, in another thread, "Building your own ISP adapter" I have posted my idea on how to build a programming adapter for the SX28 - maybe, this helps if everything else fails (you would need to modify it for your 5-pin header though).

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Greetings from Germany,


G

Peter Verkaik

I checked with the manual,

for debugging no external clock source of any kind must

be connected to the osc pins.

Can't you severe the track at the pcb (you only need 0.1" distance)

and solder a two-pin header on the cut ends?

If you're still designing: Because you use an external clock driver,

there is no real need to have the shortest track, you could reroute

the clock signal to where you can put a jumper.

regards peter

Stephen

Please remember that for debugging, the SX-Key must have complete control of the clock. This means no other clock source can be present on OSC pins. Also, as the SX can trigger off some pretty quick edges, the SX-Key in debug mode will be outputing it's clock onto the OSC pin, at the same as the oscillator output, resulting in a summed frequency of who knows what! The SX just clocks off an edge, at whatever rate... It could end up trying to execute at far greater clock speed than you intend, or at best simply die.

simon

@G