Dobbertin Smart Watch

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The Dobbertin Smart Watch was produced by Dobbertin Industrie Elektronik, a German company. This real time clock was relative wide spread in the 80ies and 90ies.


The SmartWatch consists out of the RTC itself and an EPROM expansion with a lot of RSX commends. The RTC itself was inserted like an EPROM in any kind of ROM or EPROM card. Further it contains a little battery. At least one clock is still running in 2014!

Dallas Semiconductors SmartWatch


The 28pin SmartWatch (DS1216) is an adapter that can inserted in standard ROM sockets, a ROM chip can be mounted on the adapter, finally, inside of the adapter is a 16pin Phantom Time Chip (DS1315). Normal memory reads are forwarded to the piggyback ROM. After reading from a specific sequence of addresses, the ROM is disabled, and data is instead read from the Phantom Chip via 1bit databus. Writing to the Phantom Chip is done by reading from a specific sequence of addresses, too.

64bit packets

Accessing the RTC is done by following steps

  • Read 1 or more bits (this resets the recognition pattern; best read at least 64 bits, in case the chip was in the 64-bit data read phase)
  • Write the 8-byte (64bit) recognition pattern
  • Read or Write the 8-byte (64bit) register data

The 8-byte (64bit) pattern/data is transferred serially, LSB first. The used bits on address and databus are:

A2 data direction (0=write, 1=read)
A0 data written to RTC, when A2=0=write
D0 data read from RTC, when A2=1=read, and only when pattern recognized

Recognition Pattern

The recognition pattern is: C5h, 3Ah, A3h, 5Ch, C5h, 3Ah, A3h, 5Ch.

Register 0..7

0  1/100 Seconds (BCD 00h..99h)
1  Seconds       (BCD 00h..59h) (Bit7=Zero)
2  Minutes       (BCD 00h..59h) (Bit7=Zero)
3  Hours         (BCD 01h..12h or 00h..23h) (Bit5=PM when Bit7=12-hour mode) (Bit6=Zero)
4  Day of Week   (01h..07h) (Bit4=Disable Reset input, Bit5=Disable OSC, stop clock) (Bit3,6,7=Zero)
5  Day           (BCD 01h..31h) (Bit6-7=Zero)
6  Month         (BCD 01h..12h) (Bit5-7=Zero)
7  Year          (BCD 00h..99h)


DALLAS DS1216.jpg The original RTC from Dobbertin.

RTCdxs.jpeg The expanded version from dxs.



  • The TimeROM Software provides RSX commands to use the RTC under BASIC.
  • Support for CP/M Plus is provided. The TIMEROM+.COM program sets the software clock according to the RTC. Please use the patched versions of DATE.COM, DIR.COM, SETDEF.COM and SHOW.COM (Y2K Patch).
  • The Smart Watch is supported by FutureOS. TFM provided some routines here.