Color Computer CoCo SDC User Manual
CoCo SDC
About the cover image:
Darren Atkinson designed the CoCo SDC hardware and soware.
http://cocosdc.blogspot.com
Printed circuit board manufactured by Ed Snider.
https://sites.google.com/site/thezippsterzone/
e clear acrylic case designed by Tim Lindner.
https://youtu.be/OdSOUcd60Ok
is manual takes inspiration from Brian Blake’s original.
COCO SDC | iii
Table of Contents
1. What is the CoCo SDC? ................................................................................... 1
Features and Specications ...........................................................................................2
Hardware Guide ................................................................................................................. 2
Jumper Settings ................................................................................................................. 3
DIP Switch Settings ........................................................................................................... 3
How is the SDC dierent from competing products? .......................................... 4
2. Getting Ready For Fun ................................................................................... 5
The Basics ............................................................................................................................. 5
D & E Compatibility Issues .............................................................................................. 5
Identifying the problem boards ................................................................................... 6
Motherboard Modication ............................................................................................. 6
Finding a Suitable Enclosure ......................................................................................... 7
Updating SDC-DOS ........................................................................................................... 7
Rescuing After a Failed Update ..................................................................................... 8
Recovery Steps.................................................................................................................... 9
3. Using the SDC ............................................................................................... 11
DRIVE – Mounting SD Based Images ........................................................................12
Multiple Disks .................................................................................................................... 12
DRIVE – With Wildcards .................................................................................................. 13
DIR .........................................................................................................................................14
Setting Current Directory..............................................................................................15
Explaining DIR ................................................................................................................... 15
Locking Disk Images ....................................................................................................... 16
Creating New Disk Images............................................................................................16
Ejecting a Disk Image ..................................................................................................... 16
iv | Table of Contents
Using the CoCo SDC with Drivewire .........................................................................16
Connecting via the Color Computer .........................................................................17
Accessing Real Floppy Disks ........................................................................................18
Automatic Program Execution .................................................................................... 18
EXP ........................................................................................................................................19
DEF DW = n ........................................................................................................................19
4. Using the Flash ............................................................................................. 21
Running a Cartridge Image .......................................................................................... 21
Erasing Banks and Sectors ............................................................................................ 22
Writing to the Flash .........................................................................................................22
Copying a Block of Memory ......................................................................................... 23
5. About File Formats ....................................................................................... 25
DSK Images ........................................................................................................................25
Disk Geometry Table for DSK Images .......................................................................26
JVC Images .........................................................................................................................26
VDK Images ........................................................................................................................ 26
SDF Images ........................................................................................................................27
SDF File Format ................................................................................................................. 28
Contents of the SDF 512 byte File Header .............................................................. 28
Contents of the SDF 256 byte Track Header ...........................................................29
COCO SDC | 1
1
What is the CoCo SDC?
e CoCo SDC is a home-brew project for the
TRS-80 Color Computer (CoCo). It has been in
various stages of development since 2009. e
original plan was to provide oppy controller
emulation which worked in conjunction with
the Drivewire server. at idea was eventually
scrapped in favor of a self-contained system
using an SD card.
CoCo SDC Prototyping.
A number of high capacity storage solutions
have previously been developed for the CoCo,
including a MicroSD card interface, a handful
of IDE and SCSI interfaces and the very
popular Drivewire server.
One drawback of these oerings has been
that they aren’t compatible with soware that
was written to interact directly with a oppy
disk controller. is isn’t so much a problem if
you are primarily using the CoCo for BASIC
programming or running OS9 soware.
ere are however a number of titles (mostly
commercial games) that fail to work with those
other systems.
e CoCo SDC aims to solve the compatibility
problem by combining the traditional “soware
hook” approach with a robust emulation of
the oppy controller in hardware. is dual
mode implementation provides excellent
performance for the majority of soware which
“plays by the rules” while adding a high degree
of compatibility with those titles that employ
oppy-based copy protection schemes or
simply choose to roll their own oppy drivers.
An enhanced LBA access mode has also been
incorporated into the rmware, allowing the
CoCo SDC to go beyond simply emulating
oppy disks and interface with virtual hard disk
images as large as 2 gigabytes. Two separate
disk images (oppy or hard disk) contained
on the same SD card may be “connected”
simultaneously.
2 | Chapter 1
CoCo SDC Revision 3 Board.
Also on board is 128K of Flash memory
which is divided into 8 banks of 16K. ese
16K banks are both hardware and soware
selectable and occupy the cartridge ROM space
from $C000 to $FEFF.
One bank of the Flash memory is used to
hold the SDC-DOS code which is yet another
patched version of Microso’s Disk Extended
Color BASIC 1.1. Included in SDC-DOS are
additional commands to mount disk image les
on the SD card, program the Flash and execute
ROM images contained in the Flash. Drivewire
disk support is also included in SDC-DOS.
Features and Specications
• Atmega 328P AVR micro controller @ 10Mhz
• Custom 512 byte boot-loader allows rmware
to be updated by the CoCo
• 128K In-System-Programmable Flash
• Accepts SD/SDHC cards formatted with
FAT16 or FAT32 le system
• Emulates a Tandy Floppy Disk Controller
• Emulate Dragon DOS oppy controllers
• LBA access mode for virtual hard disk
support
• Extensions to Disk BASIC in SDC-DOS for
disk image manipulation
• Drivewire disk protocol with auto-speed
conguration for CoCo 1, 2 or 3
• “Disk Switch” button to support multi-disk
programs
• PCB can be mounted in a Tandy FD-502
enclosure
Hardware Guide
SD Card Direction.
e SD card socket is a Push-Push type. When
removing the card, always push in to release
the latching mechanism before sliding the
card out. Never use force to pull the card out
of the socket. e card must be inserted into
the socket upside-down (label facing down,
contacts facing up). Use only SD or SDHC
cards with the CoCo SDC.
COCO SDC | 3
Insert the card into the socket before applying
power to the CoCo or Mult-Pak Interface.
When power is applied, the LED on the CoCo
SDC board should light up momentarily. If
the LED does not turn o aer a few seconds
then this is an indication that the card was not
recognized by the hardware. is can happen if
the card has not been formatted with a FAT16
or FAT32 le system. It could also indicate that
the card was not inserted properly or that there
is a problem with the CoCo SDC itself.
Although SD cards are hot-swappable, the
CoCo SDC rmware does not handle that
situation very well. It’s recommended that
you completely shutdown the CoCo and
MPI before swapping cards.
Jumper Settings
e three-pin jumper strip provides two
mutually exclusive options for board
conguration; Cartridge Auto-Start and
Dragon DRQ Mode. e default setting has
neither option enabled (no jumper installed).
Installing a jumper between the center pin
and the AUTO pin connects the Q clock to the
CART interrupt pin. is causes the computer
to automatically start executing the program in
the selected Flash bank at power-up. Do NOT
use this option to auto-start SDC-DOS or other
Disk BASIC ROMs.
Installing a jumper between the center pin and
the DRQ pin is required to support emulation
of a Dragon DOS oppy controller. Do NOT
install a jumper in this position when using the
board with a CoCo.
Jumper & DIP Switches.
DIP Switch Settings
e board includes a 4-position DIP switch
that is used to congure which bank of Flash
is active at power-up or reset and which
addressing scheme is used to communicate
with the controller.
CAUTION: Make sure the computer’s power
is o before making any changes to the DIP
switch settings!
4 | Chapter 1
ree of the switches specify the Flash bank to
activate upon power-up or system reset. e
switches are labeled on the board as 4, 2 and
1. e eight Flash banks are numbered 0 to 7.
Place only those switches whose sum equals the
desired bank number into the ON position. For
example, to select bank 5, place the switches
labeled 4 and 1 into the ON position and leave
the switch labeled 2 in the OFF position. e
board is provided with SDC-DOS in bank 0
of the Flash and all three switches in the OFF
position.
e DRGN switch selects the address scheme
for the controller. In the OFF position the
controller will use the CoCo address scheme.
In the ON position, the controller will use the
Dragon DOS address scheme. e dierent
schemes are summarized in the following table.
Usage CoCo Address Dragon Address
Drive Control Latch FF40 FF48
Flash Data Register FF42 FF4A
Flash Control
Register
FF43 FF4B
Command/Status FF48 FF40
FDC Track Register
I/O Register 1
FF49 FF41
FDC Sector Register
I/O Register 2
FF4A FF42
FDC Data Register
I/O Register 3
FF4B FF43
CoCo & Dragon Address Schemes.
How is the SDC dierent from competing
products?
• No reliance on expensive third-party
modules like the 4D systems uDrive.
• Does not use a slow serial interface based on
an obsolete part (6551 ACIA).
• True emulation of the oppy controller
hardware for maximum compatibility.
• Supports the popular Drivewire protocol for
PC-based disk images.
• Eight banks of in-system-programmable
Flash instead of an EPROM.
• Ability to “switch disks” for multi-disk
programs via a button on the controller.
• SD cards are FAT-formatted and require no
special imaging utility for a PC/Mac.
Probably the only drawback of the device is
the fact that the SDC does not come with an
enclosure.
John Strong has been known to make 3D
printed cases available. Here is his website:
http://strongware.net/author/johnstrong/
COCO SDC | 5
2
Getting Ready For Fun
The Basics
ere are a few very important things that must
be touched upon before we get into the actual
operation of the CoCo SDC:
1. NEVER insert or remove the CoCo SDC
into a CoCo that is turned on! Just like any
other device that uses a Color Computer
cartridge port, inserting the CoCo SDC into
your Color Computer can damage the Color
Computer, CoCo SDC, or both.
2. Although SD cards are hot-swappable, the
CoCo SDC rmware does not handle that
situation very well. It’s recommended that
you completely shutdown the CoCo and
MPI before swapping cards.
3. e rmware in the CoCo SDC does
not currently support long le names. You
must ensure that the names of all les and
directories which are to be accessible by
the CoCo conform to the older 8.3 naming
conventions.
D & E Compatibility Issues
e CoCo SDC is compatible with all versions
of the Color Computer and Dragon Computer
lines. However, aer getting the CoCo SDC
into the hands of some users, it was discovered
that Flash programming does not work
correctly on certain CoCo 1 motherboards. e
two earliest CoCo 1 boards known as the ‘D’
and ‘E’ boards are the culprits.
Board Identiers.
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 frontle 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.
COCO SDC | 7
e modication is rather simple and involves
cutting just one leg of a capacitor. Be sure to
disconnect power to the CoCo and discharge
any static electricity from your body before
touching any of the components inside the
CoCo. e aected capacitor is located within
the shielded area so you will need to remove
the metal cover to gain access. Find the
capacitor labeled C85 which is located next to
the cartridge port (see photo).
Using an appropriate tool, cut the front leg
(the one nearer the keyboard) of the capacitor
to sever the connection. at’s it! Replace the
metal cover, close up the case and you are good
to go.
CoCo 1 D & E board mod.
1 Available from: http://cocosdc.blogspot.com
Finding a Suitable Enclosure
Before you plug in the CoCo SDC, you should
consider an enclosure for the device. Ideally,
an FD-502 enclosure is preferred, as the FD501 enclosure is slightly dierent and requires
some modications to work properly. Both
enclosures need to be modied to provide
easier access to the DIP Switches, while the FD502 already provides easy access to the SD card
slot and the push button by the SD card slot.
e SD card slot and push button ARE
accessible, with the FD-501, however, it’s
advisable to trim some excess material from
the housing in order to make it easier to access
these features of the CoCo SDC.
Updating SDC-DOS
e SDCSETUP.DSK
1
image contains a
utility program that can be used to install the
rmware for a CoCo SDC controller. Both
the micro controller code and the SDC-DOS
(Disk BASIC) ROM image can be installed
using this utility. When using a CoCo 1 or 2 a
minimum of 32K RAM is required to perform
an installation of SDC-DOS and 64K RAM is
required to install the MCU rmware.
e disk image may be copied to an SD card or
accessed via DriveWire. With the disk image
mounted, run the utility by entering:
RUN "SETUP"
8 | Chapter 2
You will be presented with the following menu
options:
V DISPLAY INSTALLED VERSIONS
F INSTALL MCU FIRMWARE
D INSTALL SDC-DOS
Q QUIT
Press the V key to display the version
information of the soware currently installed
in the CoCo SDC controller. is will display
both the MCU rmware version and the SDCDOS version.
If your rmware is older, press the F key to
begin the process of installing the ATmega
MCU rmware. is will rst load the
rmware into memory and perform a
checksum validation. e version number of
the rmware to be installed is also displayed.
Before installation begins you will be asked
for conrmation by pressing the Y key. Aer
installation is complete the CoCo will re-boot.
Press the D key to perform an installation of
SDC-DOS. is will rst load the ROM image
into memory and ask which of the 8 Flash
banks should be used as the destination. You
may install over the version of SDC-DOS
that is currently running if so desired. When
installation is complete the CoCo will re-boot
using the newly installed version (switching
banks if necessary).
Boot screen for SDC-DOS.
Rescuing After a Failed Update
is is mostly for folks who have attempted
an update on a D or E board CoCo 1, and
ended up with a CoCo SDC that will only
boot to DECB. e recovery steps should be
performed on either a modied D or E board
CoCo 1, a CoCo 2, or a CoCo3 – as long as
the DIR command hasn’t been issued with any
arguments prior to attempting the update.
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