6 | Chapter 2
e Cartridge Select Signal (CTS) on these
boards exhibits too slow of a rise-time which
causes problems for the high-speed Flash chip.
is does not aect normal operation of the
CoCo SDC in terms of being able to read data
or execute code from the Flash. When writing
to the Flash however, the slow rise time oen
results in incorrect data being stored in the
chip.
ere are a few options to deal with this
problem:
1. Do not use a CoCo 1 with one of the
aforementioned motherboards to program
the Flash. is option is not ideal, especially if
you don’t have another suitable CoCo in your
possession.
2. Use a Multi-Pak Interface when
programming the Flash. e signal buering
in the MPI acts as a kind of lter for the CTS
line, producing a nice clean transition. is is a
good option if you do not wish to modify your
CoCo and you happen to own an MPI.
3. Perform a simple modication to the CoCo
1 motherboard to x the problem (see details
below).
Identifying the problem boards
To determine if your CoCo 1 has one of the
problematic motherboards you will need to
open the case and look inside. e boards in
question have a large metal shielded area that
encloses all of the main logic chips including
the RAM, CPU, SAM, VDG and PIAs. ere
should be a number printed on the board just
below the cartridge port which ends with “-D”
or “-E” as seen in the photos below.
If your board has a smaller RF shield which
only covers the SAM and RAM chips, or has a
number printed on the board (near the front-
le corner) that ends in ‘285’ then this is what
is oen referred to as the ‘F’ board. e ‘F’
board does not exhibit the problem and needs
no modication.
Motherboard Modication
Please note that any modication to the CoCo
is performed at your own risk. Although it
is highly unlikely that this modication will
cause any problems with other hardware, I can’t
be held responsible for any damage or loss of
functionality that may occur should you choose
to go through with it.
