Renesas R8C Start up problem

Do you have a question? Post it now! No Registration Necessary

Translate This Thread From English to

Threaded View
Hi,
I have used LM1086-3.3 lowdrop regulator and R8C cpu. Reset circuit is
only pull-up.
CPU doesn't start up right. External oscillator doesn't run when I turn
on  power. If I reset the CPU externaly everthing is OK.
Can you recommend something?


Re: Renesas R8C Start up problem
On 14 Oct, in article

Quoted text here. Click to load it

What no cap?

Quoted text here. Click to load it

Put a cap between pull up and ground.

Are all parts (pull-up, cpu and external oscillator) on the SAME power
rail.


--
Paul Carpenter          | snipped-for-privacy@pcserviceselectronics.co.uk
<http://www.pcserviceselectronics.co.uk/ PC Services
We've slightly trimmed the long signature. Click to see the full one.
Re: Renesas R8C Start up problem
there is a capacitor between reset pin and gnd, also there are 10uF and
some 100nF between Vcc and GND. all component power line is same.
Xout pin -one pin of oscillator- connected to CPLD.

What a stupid problem.

Thanks


Re: Renesas R8C Start up problem
Problem is values of resistor and capacitor on the reset circuit. 22K
and 100nF are true values


Re: Renesas R8C Start up problem

Quoted text here. Click to load it
and

Maybe the problem is not with the Reset pull-up, but with Vcc ramping up
too slow.  10uF is not extremely large, but if power leads are long the
LC combination may make Vcc ramp up too slow when you apply power.  I've
had problems with this when tinkering around and using long, skinny clip
leads to connect power.  Also perhaps not enough capacitance on external
osc to start reliably.


Re: Renesas R8C Start up problem
Quoted text here. Click to load it

At least in R8C/1x series the external osc is not supposed to start when
you reset the CPU. It must be started by firmware.
Also, the built-in reset circuit in R8C/11 and /13 is designed to
operate at +5V - check is parameters in the data sheet. For 3V operation
an external RC circuit is needed.

Re: Renesas R8C Start up problem
Quoted text here. Click to load it

Hi The damn thing giving me the same problem.
there is a pull up resistor 5k from reset pin to vcc. vcc 5v
manual grounding of reset is not working , power on reset not working
some times it resets but rarely.
is there a desing problem in the renesas ?
Narender





Re: Renesas R8C Start up problem

Quoted text here. Click to load it

Perhaps you need an RC on reset pin.
Add a 1uf cap from RESET to GND and see if that helps.



Re: Renesas R8C Start up problem
Quoted text here. Click to load it

Which R8C variant do you use?
Some (like /12) don't provide internal reset at all. Some may use reset
ONLY if supplied from 5V. Only the new ones from /2x family provide
internal reset at lower suply voltages and only if the rising time
condition is met.

Re: Renesas R8C Start up problem
Quoted text here. Click to load it

What is a 'desing problem'?

--
 <http://www.cs.auckland.ac.nz/~pgut001/pubs/vista_cost.txt
 <http://www.securityfocus.com/columnists/423
We've slightly trimmed the long signature. Click to see the full one.

Site Timeline