

         by Scott Peterson.

(Note: ANALOG Computing has NOT tried this modification to the 130XE and is
presenting this file for your information only. Try this hardware
modification at your own risk!)

After both reading and building both the 800/288K upgrade (D.G.Byrd), and
the 800XL/256K upgrade (C.Buchholz), I desided that there also had to be a
way to upgrade the 130XE. There is, and thanks to the "Freddie" chip
(CO61991) this modification is much easier to do than either of the other
upgrades.

To do the upgrade you will need a soldering iron, a de-soldering tool,
and some fine wire. See the parts list for the chips needed.

First, remove both the case and the metal shield to get down to the
mother-board. Then remove the eight ram-chip U26 thru U33 (MT4264). 
They are the row closest to the TV RF module. Next, install Z2 thru Z9 in
the place of U23 thru U33. These are the 256K ram-chips. You can solder
them to the mother board, or use sockets. Now take a piece of wire
approx 12 in. long and run a jumper from pin one on each of the 256K
ram-chips to the next. After you do this the wire will be connected to
pin 1 on Z2 thru Z9 and you should have about 6 inches left over. Do
this on the rear of the mother board and then snake the wire thru the
large hole near the ram chips.

Next, desolder and remove U23 (CO14795), and replace it with a 40
pin socket. Bend up pins 15 and 16 on U23 and insert it in the socket you
just installed. Take Z1 (74LS158) and bend up all the pins on it except
pins 8 and 16. Put this "piggy-back" on top of U20 (HD14050) and solder
pins 8 and 16 of Z1 to pins 8 and 16 on U20. Now solder a short jumper
from pin 15 on Z1 to pin 8 of Z1.

Now, take a piece of wire about 4 in  long solder one end to pin 30 on the
chip marked "CO14805" on the mother board, and the other to pin 1 on Z1.
Next solder a wire to pin 15 (one of the two you bent out) of U23 and
connect the other end to pin 2 on Z1. Solder a wire to pin 16 on U23 and
connect the other end to pin 3 on Z1. Take R1 (33 ohm) and trim the leads
to about 1/4 in. Take the wire you connected to pin one on the 256K
ram-chips and solder it to one end of R1, solder the other end of R1 to pin
4 on Z1. Re-assemble the RF shield and base and you are finished.

             PARTS LIST
             ----------

1) Z1    74LS158 (2 to 1 Multiplexer)
8) Z2-Z9 41256 dynamic RAM (150ns)
1) R1    33 ohm 1/4 watt resistor
1)       40 pin socket
8)       16 pin sockets (optional)

The next page is a quick overview of the bit table and numbers to be used
in location 54017 (PORTB). I have finished modifying a ramdisk handler
for the extra ram. It uses a ram based OS so basic XE or XL can't be
used. At present the best deal for this mod. is to use MYDOS 4.0. This
supports a very large single density ramdisk. With basic XE you can use a
1500 sector ramdisk and without it you can have about 2000 sectors.

This upgrade has been built and tested on a BBS, it has run for days
on end without a memory loss or error. If you need help or more
information feel free to call the Peanut Gallery (408)-384-3906. 24HR,
300/1200 Baud. Leave mail to the Sysop(thats me). Good luck and let me
know if you write a better handler.

Memory Control Register 54017 ($D301)

    Bit 7 6 5 4 3 2 1 0
        D a b C c d B R

D=0 enable diagnostic ROM.
B=0 enable BASIC ROM.
R=1 enable OS ROM.
C=0 enable extended RAM.
abcd= memory control bits.

--------------------
Bank #   Control#
--------------------
Bank 0 -------->131|
Bank 1 -------->135|
Bank 2 -------->139|
Bank 3 -------->143|
Bank 4 -------->163|   Basic= off
Bank 5 -------->167|   OS   = on
Bank 6 -------->171|   ENH  = on
Bank 7 -------->175|
Bank 8 -------->195|
Bank 9 -------->199|
Bank 10 ------->203|
Bank 11 ------->207|
Bank 12 ------->227|<--\		$e3
Bank 13 ------->231|    \		$e7
Bank 14 ------->235|    / 130XE		$eb
Bank 15 ------->239|<--/   bank's	$ef
--------------------

If you are using MYDOS 3.016 and wish to use Basic XE and a ram-disk at the
same time, boot DOS and poke 5275,163 and 5324,16. Go to DOS and write the
new DOS. This will keep the two from "bumping" into each other. A similar
poke can be done t0 DOS 2.5, it is poke 4838,163. The handler I have
will set up 192K of the extra ram as 2 SD ramdisks or 1 DD ramdisk.

If you are a hot-shot programmer (I'm not) I think a print spooler that
uses part of this ram would also be very nice. This mod is easy to do and
perfect for running a BBS. One note, on compuserve there is a mod by Rich
Andrews which should not be confused with this one, his uses 33 new chips
and mine uses 9 new chips. Have fun.

Scott Peterson


