Portion from a 1989 Radio Shack catalog
The SmartWatch was a single-chip clock/calendar add-on that could be used by many computers, including the TRS-80 Model I, III, and 4. The SmartWatch chip, a Dallas Semiconductor DS1216E, worked by replacing a 28-pin ROM and plugging the chip into its socket. Installation varied depending on the computer, but the general steps were simple:
- remove a ROM chip from the computer
- plug the ROM chip into the SmartWatch
- plug the SmartWatch into the empty ROM socket
Radio Shack sold the SmartWatch for the Model 1000, 1200, and 3000 as catalog number 25-1033. Although Radio Shack never actually sold the SmartWatch for any TRS-80 models, that same package could be used on the Model I, III, and 4 and the Color Computer with appropriate software.
Installing the SmartWatch on a Model I, III, or 4 was fairly simple, requiring only that a jumper be used to connect two pins of the chip. The TRS-80 SmartWatch drivers that most people used, CLK1/CMD, CL3/CMD, and CLK4/CMD, were written by Duane Saylor. They worked on a wide range of operating systems, including LS-DOS, LDOS, DOSPLUS, NEWDOS/80, and TRSDOS 1.3.
The SmartWatch battery was only rated to last ten years, but I have one that is twenty years old and still going strong. Dallas Semiconductor, now a division of Maxim Integrated Products, still sells the DS1216E, making it one of the few TRS-80 add-ons still available today.