ROM serial

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Many of the simpler chess computers generally use a microcontroller (MCU, from MicroController Unit), instead of a microprocessor combined with other integrated circuits and discrete components.

A MCU is a small "computer" on a single chip, and contains a CPU along with RAM, ROM, programmable input/output peripherals, etc. Certainly a MCU can access external RAM and/or ROM, but this is beyond the scope of this article.

Some MCUs do not include ROM, but those that do, usually indicate a "ROM serial" written on the chip package, often within the MCU's own reference. This "ROM serial" is specific to each manufacturer and MCU family. But it uniquely identifies the code contained in the ROM. That is, two MCUs with the same "ROM serial" will contain identical data in the ROM.

For example, we can know that Mephisto Europa, Mephisto Europa A and Mephisto Marco Polo have the same ROM because the "ROM serial" of their MCUs are identical (E62). There are other cases where the "ROM serial" will be different even though we consider the chess computers as clones because they have the same chess program, as could be the case of Novag VIP and Novag Primo, but this is because the ROM contains not only the chess program (opening book, chess engine...) but also the program code needed to control the inputs and outputs, and VIP has only a keyboard without a sensory board, while Primo has a sensory board, and therefore their ROMs cannot be identical: hence their "ROM serial" cannot be the same.

Let's take an example with a Hitachi MCU from a SciSys chess computer:

The example above is a Hitachi HD6301Y0 MCU, manufactured for SciSys.

In the upper half is the SciSys information, where we can see the chess computer model "SX5A". It could be the case that two MCUs with the same model reference have different "ROM serial", for example due to a small change in the ROM data, perhaps because of a bug fix.

In the lower half are Hitachi's own data, where we can see the "ROM serial" (A96 in this case) discussed in this article, as well as other manufacturing data.

Important: The "ROM serial" is specific to each particular MCU (to each Product Name). For example the rom of a Hitachi HD6301Y0 with "ROM serial" A99 does not have to be the same as the rom of a Hitachi HD6301X0 with the same "ROM serial". The same happens for example for a Hitachi H8/325 and a H8/3214.


The above also applies to MaskROMs, a type of ROM whose contents are programmed by the Integrated Circuit manufacturer, rather than by the user (the manufacturer of the chess computer, in our case). Some MaskROMs have a "ROM serial", and in some cases, although it is not the most common, two different chess computer models could have the same MaskROM.

Below is an example of the MaskROMs of the Novag Super System III chess computer, where can be seen the "ROM serial" C19082 and C19081E used by Synertek: