Forums

Clock output from LPC2138

Started by prer...@gmail.com January 17, 2011
Hello there - I need to interface LPC2138 with an external device (Coolrunner CPLD), and would like to keep a common crystal for both. For LPC2138, if I keep in osc mode, it is using XTAL1 and XTAL2 as crystal input pins. My question is, if I want to supply a 12 MHz clock from LPC to CPLD, how should I do it? Your help is highly appreciated... (btw, I tried google for past few days, but could not find a simple understandable answer, and so this forum)
- Prerak

An Engineer's Guide to the LPC2100 Series

--- In l..., prerak.sheth@... wrote:
>
> Hello there - I need to interface LPC2138 with an external device (Coolrunner CPLD), and would like to keep a common crystal for both. For LPC2138, if I keep in osc mode, it is using XTAL1 and XTAL2 as crystal input pins. My question is, if I want to supply a 12 MHz clock from LPC to CPLD, how should I do it? Your help is highly appreciated... (btw, I tried google for past few days, but could not find a simple understandable answer, and so this forum)
> - Prerak
>

Did you check section 4.4 of the User Manual?
http://www.nxp.com/documents/user_manual/UM10120.pdf

Richard

On Mon, 2011-01-17 at 09:09 -0500, p...@gmail.com wrote:
> Hello there - I need to interface LPC2138 with an external device
> (Coolrunner CPLD), and would like to keep a common crystal for
> both. For LPC2138, if I keep in osc mode, it is using XTAL1 and
> XTAL2 as crystal input pins. My question is, if I want to supply
> a 12 MHz clock from LPC to CPLD, how should I do it? Your help is
> highly appreciated... (btw, I tried google for past few days, but
> could not find a simple understandable answer, and so this forum)
> - Prerak

Hi Prerak,

Did you look into a seperate oscillator feeding a 12MHz
signal to the lpc and cpld ?

roelof

I'm using a 2148 with a Coolrunner CPLD. My CPLD doesn't require a
clock. Which one are you using?

Sutton
Sutton Mehaffey
Lookout Portable Security
4040 Royal Dr.
Kennesaw, GA 30144
770-514-7999, 800-207-6269
Fax: 770-514-1285
http://www.lookoutportablesecurity.com
s...@lookoutportablesecurity.com

On 1/17/2011 9:09 AM, p...@gmail.com wrote:
>
> Hello there - I need to interface LPC2138 with an external device
> (Coolrunner CPLD), and would like to keep a common crystal for both.
> For LPC2138, if I keep in osc mode, it is using XTAL1 and XTAL2 as
> crystal input pins. My question is, if I want to supply a 12 MHz clock
> from LPC to CPLD, how should I do it? Your help is highly
> appreciated... (btw, I tried google for past few days, but could not
> find a simple understandable answer, and so this forum)
> - Prerak
On Mon, 17 Jan 2011 14:14:37 -0000, you wrote:

>--- In l..., prerak.sheth@... wrote:
>>
>> Hello there - I need to interface LPC2138 with an external device (Coolrunner CPLD), and would like to keep a common crystal for both. For LPC2138, if I keep in osc mode, it is using XTAL1 and XTAL2 as crystal input pins. My question is, if I want to supply a 12 MHz clock from LPC to CPLD, how should I do it? Your help is highly appreciated... (btw, I tried google for past few days, but could not find a simple understandable answer, and so this forum)
>> - Prerak

Use a timer match output or PWM outout to generate the external clock
From: l... [mailto:l...] On Behalf Of
Sutton Mehaffey

> I'm using a 2148 with a Coolrunner CPLD. My CPLD doesn't require a
> clock. Which one are you using?

If the CPLD only has combinatorial logic in it, then obviously it won't
require a clock. The OP said he needs a clock so it must have some
sequential logic programmed into in it.

I clock a Xilinx CPLD from a LPC2148 using a single PWM output so I can
adjust the CPLD's performance and clocking from the uC.

--
Paul Curtis, Rowley Associates Ltd http://www.rowley.co.uk
SolderCore arriving Winter 2010! http://www.soldercore.com

Hello there - I need to interface LPC2138 with an external device (Coolrunner CPLD), and would like to keep a common crystal for both. For LPC2138, if I keep in osc mode, it is using XTAL1 and XTAL2 as crystal input pins. My question is, if I want to supply a 12 MHz clock from LPC to CPLD, how should I do it? Your help is highly appreciated... (btw, I tried google for past few days, but could not find a simple understandable answer, and so this forum)
>- Prerak
>

Thank you all for your responses. I would try using a PWM channel to CPLD - the reason why I need a clock for CPLD is that I have sequential circuits using flip-flops placed in CPLD, which requires a high-speed clock.

- Prerak

Hi,

You could probably take signal from XTAL2 via some small capacitor (33pF -
100pF) to XTAL1 input on CPLD but I don't know is that in spec or out of
spec. Best way is to use discrete XTAL oscillator and feed signal to LPC2138
XTAL1 and CPLD XTAL1.

On Tue, Jan 18, 2011 at 12:30 PM, wrote:

>
> Hello there - I need to interface LPC2138 with an external device
> (Coolrunner CPLD), and would like to keep a common crystal for both. For
> LPC2138, if I keep in osc mode, it is using XTAL1 and XTAL2 as crystal input
> pins. My question is, if I want to supply a 12 MHz clock from LPC to CPLD,
> how should I do it? Your help is highly appreciated... (btw, I tried google
> for past few days, but could not find a simple understandable answer, and so
> this forum)
> >- Prerak
> >
> >
> > Thank you all for your responses. I would try using a PWM channel to CPLD -
> the reason why I need a clock for CPLD is that I have sequential circuits
> using flip-flops placed in CPLD, which requires a high-speed clock.
>
> - Prerak
>
>
>
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--
Best regards,
Mario.