                 ((( COMMODORE'S NEW RAM EXPANDERS )))


  Although the rumor is that Commodore does not intend to advertise this fact,
it is true that the new 256K and 512K Ram Expansion Cartridges are completely
compatible for use with the C-64.

  We have tested the 512K unit with both the C-64 and C-128 and found no
problems with either computer.

  The Expander Unit contains its own Command Controller and accepts storage and
retrieval commands from both computers.

  You will notice that on the back side of the shipping box, Commodore warns
that you must have a working knowledge of Basic or ML in order to use this
product.  You will also notice that it does not mention the C-64 anywhere.

  It would appear that Commodore does not want the general public to update
their C-64 but, to purchase a New C-128 in order to use this product.

  There are many advantages for the programmer but many other useful concepts
are available with these expanders.

  A good example is that many of us use Commodore Bookkeeping systems. With the
expansion cartridge you can write a Boot which will load all of the various
programs needed for your Bookkeeping system into the Ram Expander and have the
Main Program just transfer the other program modules from the expander instead
of the drive.

  The transfer speed is 1 megabyte per second and saves multitudes of time in
this type of operation. The applications are unlimited.  You simply address the
Expander with the starting and ending address of the program or information
that you wish to retrieve or store and 'WALLA', like Magic its there.


                  ((( PROGRAMMING THE RAM EXPANDER )))



  There are 11 registers in the expander.  Only ten of them are used in the 64.
They are located starting at $df00 (57088) and are defined as follows:

register 0 = status
       bits 0-3 ram expander version #.
            4 size of ram expansion.  0 = 128
                                      1 = 512
            5 verify.                 1 = verify error
            6 overflow flag.          1 = transfer completed
            7 interrupt pending.      1 = interrupt begin
register 1 = command
       bits 0-1 = transfer type.      00 cpu to ram
                                      01 ram to cpu
                                      10 swap
                                      11 verify
            2 = reserved for ram expander
            3 = reserved for ram expander
            4 = $ff00 enable.         0 = enable.
            5 = load
            6 = reserved for ram expander
            7 = execute
register 2 = low byte of computer start address.
register 3 = high byte of computer start address.
register 4 = low byte of computer end address.
register 5 = high byte of computer end address.
register 6 = ram expander bank.
register 7 = low byte of ram expander start address.
register 8 = high byte of ram expander start address.
register 9 = interrupt mask enable.
       bits 0-4 not used.
            5 interrupt on verify error.     1 = enable this interrupt.
            6 interrupt on end of transfer.  1 = enable this interrupt.
            7 enable interrupt register.
register 10= address control register.
       bits 0-5 not used.
       bits 6-7 00 inc both addresses.
                01 fix exp address.
                10 fix cpu address.
                11 fix both address.
register $ff00 config register (only on the C-128).
     A read determines current ram configuration.
     A write tells mmu what ram configuration to use.

  To execute a command, you must first set up the memory locations. Set
registers 1 and 2 with the starting address of the computer memory being used
(low / high address format).  Set registers 3 and 4 with the ending address.
Set register 5 with the 64k bank in the expander to use (there are 8 banks).
And finally, set registers 6 and 7 with the starting address in the expander to
use within the expander 64k bank.

  Then you set up the transfer type (cpu to expander, expander to cpu, etc.).
All aspects of the command register are setup before the poke is made to this
register.  The $ff00 enable flag is only set for the C128's use.  The $ff00
address in the 128 is used to determine what memory bank and address to setup
for the transfer.  It's also used to specify ram or rom transferring.  In the
64 you must set this bit to disable the $ff00 register since the 64 doesn't
have this register. The execute bit begins the transfer type.  If you are using
the C-128 then you would clear the $ff00 bit and no transfer would be made
until the $ff00 register is setup.  If this bit is set then the current memory
setup will be used.

  Here is a program example for the C-64 and C-128 that will transfer memory
between the computer and the expander with the current computer ram setup:

    10 input"Enter source, exp ram, size, bank, cmd#";s,e,b,bk,cm
    20 s1=int(s/256):s0=s-s1*256:ba=57088
    30 e1=int(e/256):e0=e-e1*256
    40 b1=int(b/256):b0=b-b1*256
    50 pokeba+2,s0:pokeba+3,s1
    60 pokeba+4,e0:pokeba+5,e1
    70 pokeba+6,bkand3
    80 pokeba+7,b0:pokeba+8,b1:pokeba+10,0
    90 pokeba+1,cm+16+128
    ready.

  The interrupt registers are used to run the ram expander through interrupts.
With interrupts, for example, you could save from the ram expander straight to
disk without passing through the computer's memory.  The address control
register could be used for many purposes. For example, you could fix the
computer's address and fill the entire ram expander with one byte value (the
byte value at the computer's starting address).

  Manipulating these registers can result in many uses for the ram expander
such as one or more ram disks or storage for very large programs sectioned into
many smaller pieces.


                    Complements of Comm-Net, Denver

                               Jon Almon
                            Charles C. Drew                                                                                                               