Thank you all very much.

I have struggled with this and tried to figure it out.  I just could not =
work out why when far jumps were made PCLATH just would not change =
immediately.

I read the manual regarding PCLATH and found it difficult to understand =
and relied on the behaviour of the registers using the simulator.  =
Confused me even more.  I tend to do a lot of that i.e. If I cant =
understand the manual I put the simulator thru its paces and see how it =
behaves.

I did not want to bother the list as I was sure it had been dealt with =
countless times.

Thanks for your time.  It is so clear now.

Regards Justin

In future I will RTFM, RTFM, RTFM ...

-----Original Message-----
From: Tony K=FCbek [mailto:tony.kubek@FLINTAB.COM]
Sent: Friday, 21 February 2003 10:06 PM
To: PICLIST@MITVMA.MIT.EDU
Subject: Re: [PIC]: PCL & PCLATH


Hi,

Richards Justin wrote:
>I am using MPLAB 6.12 and a 16f628.
>
>I got bitten by the 256 byte boundary bug.  So I relocated my RETLW
table to the last 256 bytes ie=20
>1793 to 2048
>
>When my Prog makes a call to 1793  PCL =3D 0 and PCLATH also equals 0.
If I execute the next ADDWF PCL,f  it jumps=20
>back to the start of the program.  If I manual set PCLATH to 7 in the
SIM all goes as expected.
>
>Why does PCLATH not change on the screen when it is another boundary.
Is MPLAB going astray?=20

First this is not a bug but a feature :), the PCLATH is not the 'real'
high portion of the program counter=20
it only serves as an buffer that enables writing the 'real' upper adress
counter. Therefore if one is=20
to manipulate the program counter manually you always must make sure
that the content of PCLATH are setup *before*
you write the PCL. Beacuse as soon as you write to the PCL  whatever
content is in the PCLATH
will be transfered to the PCH which is the 'real' upper program counter.
Also beware that you might
need to 'reset' the PCLATH after manipulation.

/Tony

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