this weekend I succeded in building myself a Fuse-Bit-Programmer for the AT90S1200. I have only seriell programmer hardware (which works fine for me) so I was not able to set the fuse bits in the 1200 which can only be set in parallel mode. Anyway, I used a second AVR and built myself a board with a socket where I can put the 1200 in and set the RCEN bit so that it runs on the internal RC oscillator. (Atmel Folks: The description of the parallel fuse-bit-setting in the data sheet is correct but not easy understand. A bit more explaining would have saved some of my weekends sparetime.)
My 1200's are usually used for simple PLL programming jobs in amateur radio equipment so timing is not critical.
But lets get to the point: From my vendor I can only get 1200-12 that have a guaranteed speed of 12MHz and a Vcc range of 4-6 Volts. Since it runs on the 1MHz internal clock I assume that I can use lower voltages as well since the 1200-4 works down to 2.7Volts. My guess is that the chip is the same but the 1200-12 has passed a 12MHz check. Since you need the higher voltage for the higher speed I assume Atmel simply rates them for 4-6 Volts if they guarantee the 12MHz.
The idea is to use the 1200-12 in battery powered devices with 3 cells, i.e. at supply voltages of 3.3 - 4.5 Volts without a voltage regulator.
Does anyone know if the chip is the same? If not what is the difference? Any commends from a practical point of view (do you think it will work at lower voltages)?
Have fun everyone,