On Wed, Jun 30, 2004 at 09:54:08PM -0400, Martin Klingensmith wrote:
> 1. Does Wloader work with an 877A

Not exactly. One must understand the 16F self programming hierarchy:

1) At the bottom is the simple 16F877 and bretheren (sisteren?). No erase
required and can reprogram a single word at a time.

2) Next up is the A version of these parts. In order to speed programming
efficiency program memory is written in 4 word blocks. This means a few of
things. One is that you have to write 4 consecutive words at a time. The other
is that all blocks need to start with addresses ending in 00 binary. One
other coming later.

3) Next are the newer 16F88/16F819 parts. In addition to the 16F877A
requirements, they also require that memory be erased in 32 word blocks.
And program memory cannot be reprogrammed until that erase is done.

Now for Wloader this has a few implications:

1) Your application will have issues because of addresses 0-3. And of course
all applications use these. The problem are that while the original 16F877
could write locations 0-3 (or actually a saved copy of them ) individually,
the others higher up in the hierarchy must write them as a block. The
original wloader would write address 0-2 in the save area and address 3 in
its original locatation (because wloader itself occupies. But because of the
4 block write requirement, both of these fail badly. 0-2 never get written
to the save area (no address 3 to complete the block), and the write to 3
(which does work because the address ends in 11) overwrites addresses 0-2
which as I mentioned are occupied by the bootloader. So you slag wloader
and your application can't run. Not good.

2) The serial application (xwisp.py in this case) needs to be constructed to
always send 4 word blocks even if some of the locations in the block do not
actually have to be written.

3) Let's not even get into the lack of row erase.

So Wouter has solved the problem at some point. I'm not sure if he ever
released that code. It probably added some restrictions like A jump is
required from address 0-3. Then force a 4 word write to the save area and
never overwrite the actual bootloader 0-3.

BTW have you tried linwload? Woj wrote it quick and dirty several years ago
as a C based Linux equivalent to xwisp for wloader. It works. I updated it
to be kinder to system resources when waiting. I have the code posted on my
page http://www.finitesite.com/d3jsys

Maybe you can use it as another test point to see if you can load.

Hope this gives you some insight.

BAJ

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