ATOM-lite Boot ROM
Author
Description
The ATOM-Lite BOOT ROM is for use with the ATOM-lite hard disk interface to automatically boot B-DOS from the hard disc..
It is a 32Kbyte image that can be blown onto a 27xxx pin compatible chip such as the AT27C256R, speed can be anything lower that 150μs.
General Information:
The ATOM-Lite BOOT ROM is a version 3.0 Basic ROM which will boot the DOS from hard disk or floppy disk automatically when the SAM is turned on or reset.
This ROM will also reset the SAA sound chip directly after a reset and defines the function keys F7 as DIR [RETURN] and F8 as DIR PEEK SVAR 7 [RETURN] instead of the tape commands.
Great care was taken to add these features and keep the ROM fully compatible with the original 3.0 ROM. For this reason the original copyright message had to be removed. The copyright message now will be ‘AL BOOT V2.2’ (After NEW and DOS is already in memory).
How It Works:
When the SAM is turned on or reset, the SAA sound chip is reseted and the normal reset procedure is continued. Holding the SHIFT key down during reset will give you a 256K SAM to work with. Before the copyright message is printed a test is made if DOS is in memory and if not it will fool basic that key F9 is pressed and the DOS is booted.
The BOOT command works in the same manner as before from the first attached unit, but now supports booting from any of the four possible (bootable formatted) CF cards. The forced boot is done by holding the keys 1 to 4 during the start-up of the computer (or 0 for no boot).
It is still possible to boot from floppy disk by holding down the SPACE BAR during reset or by disabling the hard disks bootsector (see below).
Making the hard disk bootable:
To make the hard disk bootable the following has to be done:
- Blow an 32kB EPROM with the ATOM-Lite BOOT ROM BIN image.
- Replace the SAM ROM with the ATOM-Lite BOOT ROM.
- Make a boot record.
- Initialise boot sector with the ‘MakeBoot’ program.
Installing the ATOM-Lite BOOT ROM
Disconnect all leads from the SAM and turn it upside down and remove all screws (except those at the plastic label in the middle). Remove the floppy disk and turn it again).
Now lift the keyboard about a cm and then pull it a cm forwards (front side). Now you can lift the front side just far enough to put your hand between it. Before doing so have a look.
You can see two green keyboard leads. One in the middle and one to the right. Pull the one in the middly out of its connector first. After that you can lift the top a bit more so you can reach the other lead. Pull it out also.
After both leads are removed. You can lift the top and put it in a save place.
Just above the middle keyboard connector you can see the SAMs ROM. Remove it by using a small screw driver as a lever.
Put the screw driver at the a side of the ROM and push it Slightly so the ROM gets loose from its socket. Do it also at the otherside and repeat this until the ROM is out of it
socket.
Now take the ATOM-Lite BOOT ROM and put it in the ROM socket. Make sure the ROM is placed with the small notch pointing to the ASIC (black square chip with VLSI in it).
After this re-assemble the SAM.
Making a Boot Record
A boot record is nothing more than a record containing a DOS at the start of a record. Just as with a bootable floppy disk.
Any Record can be used to make a boot record. But record one is recommended because it’s faster.
To make sure the DOS will be at the beginning of a record, use a empty record. When the record isn’t empty. The files in it can be copied to a other record and then be erased, copy B-DOS to it and copy the files back to the record.
In most cases copying and erasing the first file in a record will work too.
Boot Sector
The first sector of the hard disk is the boot sector. This sector contains a small machine code program to load the DOS from the boot record and sets some user definable DOS variables.
If the boot sector hasn’t been initialized, is disabled or if there is no bootable DOS in the boot record. The ATOM-Lite BOOT ROM will try to boot DOS from a floppy disk.
The boot sector is not created by B-DOS. But by a seperate program called ‘MakeBoot’ You will find it on the B-DOS disk.
Powering up note:
Once power has been switched on and the hard disk has finished its self test / initialization. The ATOM-Lite BOOT ROM will boot from hard disk.
Sometimes after the power is switched on, it may happen that the ATOM-Lite BOOT ROM boots from floppy instead of hard disk once in a while. When this happens just press the reset button.
Instructions
Installing the AL+ BootROM
The AL+ BootROM is a replacement ROM for the SAM Coupé that will make the SAM start up faster than usual and boots directly from a Compact Flash Card in Any AL+ interface from any CF-Slot. To replace the ROM in your SAM Coupé you need to open your SAM. There are no worries for breaking any warranties on your SAM anymore. But care should be taken not to damage the fragile keyboard leads. Please read the instructions below carefully.
Opening the SAM Coupé
Open the SAM Coupe by turning it upside down and then unscrew all the screws on the bottom. But not those on the MGT serial number sticker. Use a small philips screwdriver. Do not use a screwdriver that is too small or too big otherwise you may damage the screws. If you have any disk drives in your SAM then remove these before you turn your SAM around. You don’t want them to slide out while you turn your SAM around.
Lift the cover of the SAM by one or two inches by holding it at the left and right side then move the cover about half an inch backwards and put the cover down.Now raise the cover just at the front by two or three inches so you can look into the opening. You will see two leads coming from the keyboard in the centre that are connected to SAM’s circuitboard. These need to be pulled out of their sockets with care.
Keep the cover steady with one hand and use your free hand to slide through the opening. Do not lift the cover higher then 3 or 4 inches or you may put too much strain on the keyboard leads. Remove the lead closest to the front first. Put your index finger behind the lead in the middle and your thumb in the front hold the lead firmly and pull it out in a vertical motion. Do not bend or twist the lead.
With the front lead removed you can raise the cover a bit further so you can reach to other lead and pull it out the same way. When both leads are pulled from their sockets you can take the cover off. With the cover removed you can have a good look at the T shaped circuit board. In the middle is a square chip with the text VLSI. That’s the is the ASIC. Right next to it at the right is the ROM you have to replace
Replacing the ROM
The SAM ROM can be removed from its socket using a IC puller or a small flat screwdriver. Use the flat screwdriver as a wrench. Lift the rom a little at each side and continue doing this until the ROM is completely out of its socket. If the capacitor at the right of the ROM is blocking the way then you can gently bend it towards the circuit board to get better access.After the ROM is removed you can push the AL+BootROM into the ROM socket. Make sure that the small notch on one side of the Boot ROM is pointing towards the ASIC .
With the AL+ Boot ROM fitted connect power and the TV or Monitor cables and power up to check the ROM works correctly. You should see a familiar rainbow screen with the boot ROM version number. When you have you can put SAM back together following the earlier steps in reverse order. When at the point of reconnecting the keyboard leads you may decide to connect power and the TV or monitor cables again and check that all the keys function properly. When the keyboard is OK you can remove the power and monitor cables again and continue assembling.