I am currently trying to learn more about watches and what it takes to build them. I currently own a watch called the G-Shock 7900b and was wondering what runs it inside. Here is a link to the watch:


I am wondering if this uses an ASIC or a FPGA? I looked all over the internet but have had no luck finding an answer. Some of the features include receiving radio signals and having preset dates coded into the watch until 2099. Does this mean that this watch has memory? I always assumed that watches did not have a processor or memory.

Any suggests to these questions?

  • 1
    \$\begingroup\$ If they didn't have memory then how would they remember what numerals they're supposed to be displaying? \$\endgroup\$ – Ignacio Vazquez-Abrams Apr 21 '15 at 3:31
  • \$\begingroup\$ That is very true. I assumed that there were maybe little cells that helped remember the states but thats it. What kind of memory would be present in a watch such as this? \$\endgroup\$ – user081608 Apr 21 '15 at 3:33
  • \$\begingroup\$ Watches are often run by 4-bit mask-programmed microcontrollers made in special low-voltage low-power CMOS processes. They're not widely shown on the interwebs because the minimum order per code set would be something like 50-100K pieces. \$\endgroup\$ – Spehro Pefhany Apr 21 '15 at 3:38
  • \$\begingroup\$ Those "little cells" count as memory. \$\endgroup\$ – Ignacio Vazquez-Abrams Apr 21 '15 at 3:44
  • \$\begingroup\$ So would there be a processor on a watch like this? Or would that only be necessary for a smart type watch? \$\endgroup\$ – user081608 Apr 21 '15 at 3:49

The watch runs either on special ASIC (if volume is very high), or on MCU (microcontroller), often the supercheap version of MCU which is mask programmable and which uses very low clockrate (less than 1MHz)

They do have memory, but often very little of it -- a small MCU might only have 16 bytes of memory (as registers), while ASIC would only have enough memory bits to store current time and any applicable alarms.

Here is a link to a very simple watch ASIC: http://www.integral.by/eng/download/1077/IZ6199TSe.pdf . Note that this chip comes as a bare die, 1.4x1.2mm big. It will be encapsulated in the black epoxy blob on the actual watch PCB.

G-Shock may also run a bigger ASIC or an MCU; it will also be encapsulated in epoxy, but information about it is proprietary and will not be published anywhere.


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