The Difference Between A PROM and FlashROM board

The latest release of the AD-600A has a FlashROM on the circuit board, whereas the older models come with only a PROM. What is the difference? As far as the player is concerned there is no difference. They both have the same memory capacity and can store the same firmware, but electrically there is a slight difference with two of the pins. You can not just put an EPROM into a player that has a FlashROM installed.

Take a look at these two ES4318 processor boards:

At first glance there is no difference. Right? Wrong! The left side is a FlashROM fitted player while the right side is a PROM fitted player. But they look the same... Correct, but look closer. There are two ways you can tell the difference:

Method 1
The left one says (once you remove the sticker) "MM29F040" and the right one says "AT27C040". This may not mean much to you BUT if you have a look at the datasheets on these chips, the 29F040 is a 4Mbit FlashROM and the 27C040 is a 4Mbit PROM.

Method 2
Notice the orange rectangles. For the FlashROM fitted player there are resistors installed at locations R42 and R81 and locations R41 and R80 are blank. For the PROM/EPROM fitted player it is the reverse: R42 and R81 are blank while R41 and R80 have the resistors. Does this mean a ES4318 PROM/EPROM fitted player can have a FlashROM fitted? Yes it does. More information on how to do that HERE.

For the ES4308 processor player they never came out with a FlashROM factory fitted, only a PROM. However they also have the resistor options for a FlashROM as shown here:

On a PROM/EPROM fitted player the resistors are installed at locations R41 and R46 while R42 and R44 locations are blank. If a Flashrom has ever been fitted (unlikely) the resistors will be reversed: R41 and R46 blank while R42 and R44 locations will have the resistors. Does this mean an older ES4308 player can have a FlashROM fitted? Yes it does. More information on how to do that HERE.

I will back up a bit here. Some of you may be saying "PROM? EPROM? FlashROM?..... What the heck is he talking about???"

OK... The right side of the ES4318 board picture is a PROM, which stands for Programmable Read Only Memory. This is the chip that stores the program that tells the ESS processor what to do, also called the "firmware". The bad news is a PROM can only programmed once. If you make a mistake in the program, or you want to change the program (ie upgrade your firmware) then bad luck. Throw it out and buy a new one.

Once you get sick of throwing out PROM's you may want something that you can erase and use again and again and again. Hey presto.... You have an EPROM, which stands for Erasable Programmable Read Only Memory. These chips have a window in them and you can see the memory cells where the program is stored. The window is there so you can expose the chip to Ultra Violet (UV) light. UV light from a commercial EPROM eraser will blank the chip in about 10 to 15 minutes. Once the chip is blank you can then program it again. EPROM's have a minimum of 10,000 erase/program cycles so you can play to your heart's content without wearing the chip out. A picture of an EPROM can be found on my "Dual Boot" page.

This is all very well, but to change the program you have to expose the chip to UV light and wait for about 15 minutes. Wouldn't it be nice if you could re-program the chip "in circuit" (ie not have to remove the chip from the board)? You can. Welcome to the FlashROM. This is the 29F040 chip on the above left ES4318 board picture. The FlashROM is a dream. Just like the EPROM you can erase them and re-program them BUT no UV light is needed. How is the erasing done? Electricity. And if done right the chip never has to leave the circuit board (like with BI-600E and GK600 firmware). The FlashROM has a closely related cousin called the EEPROM which stands for Electrically Erasable Programmable Read Only Memory.

So how does this all relate to the AD-600A player? Simple. The latest release comes with a FlashROM fitted to the board, while the older players (both ES4308 and ES4318 player's) have only a PROM fitted, as indicated above by the resistor locations.

This is both good and bad... Good because you can re-program the FlashROM without having to buy another chip. Bad because FlashROM fitted player's can not use an EPROM just by plugging one in. So if you have a FlashROM fitted player but you want a "Dual Boot" EPROM in your player you will have to be prepared to move those two resistors as shwn in the pictures above. This is not really a hard task if you are OK at soldering. If not get someone to help you. More information on how to make a FlashROM work in a PROM player and vice versa HERE.