Introduction
AtoMMC2 provides modern mass storage for the classic British Atom
computer. It is a combination hard/software solution designed to fit
inside the Atom's case without modification to the machine. It provides
full read and limited write access to files on a FAT formatted MMC or
SD/SDHC card. It will work on any Atom computer as it doesn't require
RAM, ROM or hardware expansions.
Read on or jump to:
Installation
The interface attaches to PL8, a 20 pin dual-row header on the Atom's
mainboard. This header was not supplied with kits nor was it fitted by
default in production machines. It is a very simple job to fit, if
required, but take care to locate it pins up on the keyboard side
of the main board, where the white outline is present, not on the
component side.
With the connector on the wrong side the pin ordering will be reversed and
damage to Atom and interface will occur.
The header and interface are connected by the 20 way wire jumper. The
interface connector can only fit one way and it would be awkward to fit
the Atom end of the cable incorrectly but just in case please note the
small triangle on the cable connector. This indicates pin 1. The
location of pin 1 on PL8 is indicated by a small white dot. The card
socket dongle can only be connected one way.
In order for the firmware to initialise on reset it is necessary for
the Atom to receive interrupts generated by the interface board. This
requires the fitting of a short wire link located to the right of PL8 -
otherwise known as LK3. Without this connection the firmware will have
to be initialised manually by typing the following after each reset:
The interface should be firmly mounted inside the Atom's case. This may
be achieved by any method which will electrically/spacially insulate
the
interface from the Atom's main board. My recommendation is to put a
90 degree bend in the main cable and situate the interface on
the base of the case.
'Servo tape', self-adhesive
velcro strip or carpet tape are recommended fixatives. Care must be taken that
the placement of the interface will not interfere with case
fitting. The dongle may be tucked inside the case too if access to the
card
is not required or desired.
The firmware for the Atom resides in a 2532 EPROM and should be fitted
in the socket marked IC24. Orientation is indicated by the notch in the
chip's casing. It should be placed to match the chips around it. Please
ensure that the EPROM's legs are not
bent during fitting. If any do suffer an unexpected angular distortion,
then straighten the affected pin(s) by placing the chip with its legs
flat against
a solid, flat surface. Gently press the bent leg back into alignment
and try again. No damage should occur if the machine is powered up with
a bent pin, but the software will fail.
Initialisation
Once the interface and service ROM are fitted the machine can be
powered up and you should be greeted with a banner announcing the
presence of the interface.
ACORN ATOM + ATOMMC2
Holding various keys when hitting BREAK will have effects:
- CTRL will disable the interface firmware until next reset.
- SHIFT will try to execute a file called MENU.
- REPT will show additional information such
as the firmware revision and type of card inserted.
This image shows what you
should expect to see when holding REPT whilst resetting.
The files on
the card whose named begin with the letter S are being catalogued.
Adding software to the card
Files are simply added to the card using your choice of operating
system.
The 'ATOM' format is used to add required metadata to Atom files. It is
simply 16 bytes containing a copy of the file name followed by 16 bit
load, exec and length values in little endian ordering. Here's the
header from Snapper showing the 22 header bytes and the first 10
characters of the main program:
53 4E 41 50 50 45 52 00 00 00 00 00 00 00 00 00 SNAPPER.........
00 29 86 CE 00 13 0D 00 00 52 45 4D 2F 2F 20 53 .).......REM// S
Firmware reference
To see a listing of the files on the card type
*CAT
at the prompt. You may abbreviate this command to *CA., *C.
or simply * .
You may specify a wild-card character to filter the output. A
single letter is supplied as a parameter and only files beginning with
this character are displayed.
Files with their DOS hidden attribute set are never shown. Press SHIFT or REPT to
pause the listing. ESC will abort the listing.
*INFO filename
will show the metadata associated with a file. If none is present, junk
will be printed. There is no way to know if data is present or not. You
should see something like:
SNAPPER
2900
CE86
1300
This shows the load address to be #2900, its execution address to be
#CE86 and the file lenth to be #1300 bytes.
LOAD "filename"
will load the program into the currently selected text page.
*LOAD "filename"
will load the file into the location specified in its metadata.
*LO."filename"
(address)
will load the data into memory starting at the specified address. The
star-command processor allows either quoted or non-quoted names to be
used. The file's metadata is printed unless suppressed with the command
*NOMON
*RUN filename
or simply
*filename
will load and attempt to execute a program. The firmware attempts to
run all programs even if they were not intended to be auto-running. In
some cases this will produce an error in which case the sequence:
LOAD "filename"
RUN
should be used. Programs may also be loaded into the Atom by using:
*EXEC filename
This will present the file's content to the Atom as if it had been
typed. Files read in this way should be ANSI text files such as a
program like Notepad produces under Windows. This is a useful way of
entering programs which only exist as listings.
For firmware revision 1.0 saving of data has a restriction. You can
only save into an existing file of sufficient size to hold the required
amount of data.
SAVE "filename"
saves the current program.
will save the specified block of memory. The end address is exclusive -
in other words it is the address of the last byte to be written + 1.
The execution address will be set to the start address if not specified.
Files saved this way will appear to be of the correct length when
re-loaded - the metadata at the start of the file is used to determine
file size not the size-on-disk as understood by the FAT file system. A
PC utility exists to trim the excess data if required.
Consider saving a number of files of about 16K with names like 'SAVE1' for use
as required. These may then be processed (renamed,
truncated), if required, on a modern machine. A utility to do this is linked below.
Dowload the SDROM here
(versie SDROM2.2.ROM) by Charlie Robson and Kees van Oss
Dowload the SDROM here
(versie ATOMMC2-1.6.ROM) by Charlie Robson
Dowload the pic software here
(rar-file)
Example script file for a pic controller
En voor de aardigheid een blik op het Prototype
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