Msg: 2865 *Conference*

07-15-92 18:22:23

From: TRACY ALLEN

To : AL DEMMA

Subj: REPLY TO MSG #2833 (EXTRAM X4)

Dear Al,
  The extRAM X4   (XR4) works just fine with the UR-2 and with the datapac.  Or
is it a rampac that you have.  You mention upgrading it to 256k and that Ron at
Node told you it would take two chips to do that.  That may be true.  While I
(EME Systems) have taken over manufacturing the 256k rampac, I did not take
over the support for NODEs earlier products, and I don't have any schematics or
technical information on them.  I do know that they all have basically the same
directory structure and addressing schemes.  But you will have to contact NODE
directly about upgrading your older datapac (rampac?).
    
   I can send you the instructions that I am sending out with the current
rampacs.  It has a section that describes the directory structure of the
rampac. In brief, the first sector (sector zero) of the rampac is a FAT, or
file allocation table.  Starting at address zero in sector zero, you take pairs
of bytes.  Each pair of bytes describe the status of a sector in the rampac.
For example, if you read the first few bytes of sector zero and find the
sequence:  64,4,32,0,160,1,32,0,32,3,192,4,...  what does that mean?   The pair
64,4 means that the rampac is formatted.  If the 64,4 gets altered-that's bad.
The group in byte-pairs 1 and two is 32,0,160,1.  The 160 tells you that a .CO
program starts in sector 2, and the 160,1 tells you that the program does not
all fit into sector 2, but in fact it continues in sector 1.  The 32 for sector
1 tells you that this is a "continuation" sector, and the 32,0 means that is
the last continuation sector in this string, that is, it contains the end of
the .CO program that is stored starting in sector 2.  Where do you find the
name of the .CO program that is stored?  Look in the first 16 bytes of sector
2, before the actual beginning of the program.  Eight bytes are for the program
name, while the ninth and tenth bytes give you the actual length of the file in
the rampac.  Going back to the FAT, the bytes 32,0,32,3,192,4 tell you that a
.DO file (type 192) begins in sector 5 (the first 16 bytes of which tell you
the actual file name), and the .DO file continues into sector 4 and ends in
sector 3.