How To Make A "Dual Boot" EPROM
(SINGLE EPROM STYLE)
This method describes how to make a "Dual Boot" player with one 27C080 EPROM. Because this EPROM is double the memory size of what is installed in the player we can divide the chip in half and program it with two different firmware versions.
First, the standard disclaimer:
DOING THIS MODIFICATION NEEDS SOME ELECTRONICS EXPERTISE. IF YOU FEEL YOU CAN'T DO THIS MODIFICATION BY YOURSELF, SEEK ADVICE OR HELP FROM SOMEONE WHO CAN. I WILL NOT BE HELD RESPONSIBLE!
The easiest way to make your combined firmware is with ApexLogo. Get it HERE.
You can use ApexLogo to combine your firmware even if you are not going to change the background image. Here's how:
STEP 1: Make sure the "ROM File Output" is on "DOUBLE":
STEP 2: Select the first firmware to load:
STEP 3: When the firmware is loaded click on "Copy To First Half"
STEP 4: Select the second firmware to load:
STEP 5: When the firmware is loaded click on "Copy To Second Half"
Step 6: Now save your combined firmware!
Ant that is it. You will now have a 1024K file ready for programming.
Now that you have your combined firmware you are ready to make your "Dual Boot" EPROM. To do this you are going to need the following items:
(1) 27C801 8Mbit EPROM (120ns speed rating or better).
(1) 32 pin IC socket.
(1) Single Pole Double Throw toggle switch.
Some hookup wire, wire wrap wire or "ribbon" wire.
Some solder, soldering iron, drill (optional).
A Note On Speed Rating: The smaller the number the faster the access delay time of the chip. For example, an 80ns chip is faster than a 120ns chip. You can use as fast as you like (or your budget can handle!) but DO NOT USE SLOWER THAN 120ns. People have tried 150ns chips and they do not work very well.
First of all you are going to have to program your EPROM. If you have a programmer handy then you are in luck and this is easy. If not, you are either going to have to find someone who can help you out or make your own programmer. Try this design from Mike's Eprom Project Page.
Now you are going to have to familiarise yourself with the pins on the EPROM. Use this picture to guide you:
This is what an EPROM looks like. EPROM chips have a window in them and you can see the memory cells inside. The window is so you can expose the chip to UltraViolet (UV) light to erase the memory, so if you make a mistake or want to try other firmware you just erase the chip and program it again. An EPROM usually has a minimum of 10,000 erase/write cycles before something goes faulty so you can play as much as you like. Just like any other memory chip they come in all different capacities and sizes, and you must have the right type for this modification to work. The important thing to note from this picture is the notch at the top. This helps you identify where Pin 1 is. Sometimes, but not always, they can have a dimple near Pin 1 as shown by the white square.
The next thing to do is wire up the switch to the socket. Use these two pictures to guide you:
As can be seen from this picture of the underside of the socket, Pin 1 is bent up while Pin 16 and Pin 32 are kept straight. Carefully solder the hookup wire to the socket pin as close to the plastic body of the socket as possible. You must do this because if you solder too far down towards the tip of the pin, when it comes time to push this socket into the socket already on the circuit board the pins may not go in far enough to the existing socket and you may not get proper connection.
It is important to bend Pin 1 because we do not want it to make contact with the socket on the PCB. To be extra sure you can put a small piece of insulation tape or heatshrink tubing over Pin 1. Now install your EPROM into the socket making sure Pin 1 of the EPROM goes into Pin 1 of the socket.
And here is the complete package.
Pretty neat, huh? Now all you need to do is fit it!
First, let's have a look at where the BIOS chip is....
All that is left to do now is simply carefully lift your old BIOS chip out of it's socket and put in your "Dual Boot" package. Remember to note the notch in one end if the chip as indicated by the yellow highlighted picture above. You must use this as a guide because even though the chip can go in the socket both ways, only one way is correct and remember:
Putting the chip in the wrong way will damage your player, so be careful before you power up!
Once you are sure you have installed the chip correctly you can test your firmware before mounting the switch. Turn on your player and make sure it is working correctly. If it is then turn off your player, flip the toggle switch to the other firmware and turn your player on again. If this firmware is also working correctly you can now mount the switch in the back of the unit. Some people may want to just leave the switch hanging out the case. This is OK, but put some insulation tape around the switch to stop the bare solder connections shorting out on the case or any other metal! But I think it looks better like this:
Just remember you must turn off your player before touching the firmware selection switch!
For the technically minded, what this modification does is select two firmware versions from the one EPROM chip. You can do this by having Pin 1 (Address line A19) tied to +5 Volts (pin 32) or Ground (Pin 16). When Pin 1 is connected to Ground the bottom half of the EPROM's memory is selected, and when Pin 1 is connected to +5 Volts the top half of the memory is selected. This way we can neatly store two versions of the firmware in each half of the chip and select between them with the flip of a switch.
