One other thing to consider -- If you are using the internal RC
oscillator, you have read the JW part and write down the OSCCAL value at
0x3ff before you program it.  It has to be programmed back in after
every UV erasure.

Bill

-----Original Message-----
From: pic microcontroller discussion list
[mailto:PICLIST@MITVMA.MIT.EDU] On Behalf Of Spehro Pefhany
Sent: Monday, March 01, 2004 8:28 AM
To: PICLIST@MITVMA.MIT.EDU
Subject: Re: [PIC:] 12C509 problem


At 12:37 PM 3/1/2004 +0000, you wrote:
> >Is there a difference ( or several differences)
> >between a 509 OTP and a 509 Eprom?
>
>People have reported problems like this in the past, but typically in
>the reverse direction, I.E. JW->OTP.
>
>What is known to happen is that the light coming in the window of a JW
>part will initialise RAM registers to different states to the OTP
>parts. It would pay to check through your code to make sure that the
>RAM registers are being properly initialised by your program. You may
>have just got away with it in the OTP part, and another one may work
>differently.

As well, if you first programmed it with a non-working program and then
attempted to erase and program a working program, you may have a
problem, if you protected the memory. On the UV erasable (JW) parts the
protect bit is often made deliberately difficult or impossible to erase
compared to the rest of the program. This prevents re-use of the part,
except as a tie clip or something, so you have remember never to set it.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the
reward"
speff@interlog.com             Info for manufacturers:
http://www.trexon.com
Embedded software/hardware/analog  Info for designers:
http://www.speff.com

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