(c) 2009 David Wood

Writeup for the Community Information Locator Commodore 64/128 addon
cartridge

(C) 1986 Community Information Locator, Inc.

Commodore 64/128 board writeup.

This board was discovered en masse during the ECCC2009 expo on a seller's
table.  The physical description is summarized as a large cartridge port
addon that has sockets for up to 16 EPROMs and some simple logic.

It operates by selecting the EPROMs in 8k sectors, mapping them in the
External Function Rom range on the Commodore 128.  More on this below.

The board also has a watchdog timer that's enabled on powerup.  It's
important to either disable this watchdog by desoldering the bridge in the
lower left of the card, or pulling the 74ls123 chip in the lower left.

To use the watchdog, it's important to regularly access $DF00.  There is no
configuration to disable it in software and it provides no readback.

The ROM mapping is somewhat complex.  A quick summary of how the board is
mapped is below:

DE00-DEFF range:
d0	romA13 [pads enabled]
d1 	romA14
d2 	romA15 [pads to vcc]
d3
d4
d5 	/exrom

a0 	EromA2
a1 	EromA1
a2 	EromA0
a3 	bankA0
a4 	bankA1
a5 	bankA2

In detail, romA13, romA14, and romA15 refer literally to the address bits
sent to the rom ICs in the sixteen sockets.

EromA0, EromA1, and EromA2 refer to the rom address, enabling the !CS line
on the appropriate ROM chip in a selected group of ROMs.

bankA0, bankA1, and bankA2 refer to the rom bank address, enabling a group
of 8 roms to be addressed by the two pieces of information above.

For example, to select the second 8k block in rom 3 of bank 1, you should do
a write access of 2 to $DE16.

A formula to select a given 8k block is such:
poke 56832+bank*8+rom,block

To configure the hardware on the card, there are four pads.

One 'pad' is a pair of holes for a 2pin jumper.  Removing this jumper
disables the watchdog reset.

A second pad is present just above this, and controls the EPROM socket pin 1
wiring.  By default, this is wired to Vcc but can be changed to data bit 2
on the c64 bus as noted in the table above.

The third pad is near the center and was cut on the boards we discovered. 
This enables/disables the card's control of the /EXROM line on the cartridge
port.  Apparently, the pad is enabled by default.

Finally, there is a pad on the underside of the board that switches the
ROMs' A13 line between the commodore bus and software control.  This would
be useful on a C128, as it maps up to 16k for the /ROML function rom space. 
However, the author believes the Commodore 64 does not map the additional 8k
over the BASIC rom with just /EXROM asserted.


The physical locations of the ROM sockets aren't in a logical order, and are
detailed below in an ASCII approximation.  The numbers inside brackets
represent the ROM's ID by placing the bank number first followed by the ROM
number.

  [00] [03] [10] [16]
       [01] [02] [04]
       [05] [06] [07]
       [13] [12] [11]
       [14] [15] [17]

-jbevren

PS: Thanks to _Six_ for verifying my findings.