windowed (expensive) versions that were used for debugging and program development. The same chip came in (somewhat cheaper) opaque OTP packages for production. Leaving the die of such a chip exposed to light can also change behavior in unexpected ways when moving from a windowed part used for development to a non-windowed part for production. EPROM generations, sizes and types The first generation 1702 devices were fabricated with the p-MOS technology. They were powered with VCC = VBB = +5 V and VDD = VGG = -9 V in Read mode, and with VDD = VGG = -47 V in Programming mode. The second generation 2704/2708 devices switched to n-MOS technology and to three-rail VCC = +5 V, VBB = -5 V, VDD = +12 V power supply with VPP = 12 V and a +25 V pulse in Programming mode. The n-MOS technology evolution introduced single-rail VCC = +5 V power supply and single VPP = +25 V programming voltage without pulse in the third generation. The unneeded VBB and VDD pins were reused for additional address bits allowing larger capacities (2716/2732) in the same 24-pin package, and even larger capacities with larger packages. Later the decreased cost of the CMOS technology allowed the same devices to be fabricated using it, adding the letter "C" to the device numbers (27xx(x) are n-MOS and 27Cxx(x) are CMOS). While parts of the same size from different manufacturers are compatible in read mode, different manufacturers added different and sometimes multiple programming modes leading to subtle differences in the programming process. This prompted larger capacity devices to introduce a "signature mode", allowing the manufacturer and device to be identified by the EPROM programmer. It was implemented by forcing +12 V on pin A9 and reading out two bytes of data. However, as this was not universal, programmer software also would allow manual setting of the manufacturer and device type of the chip to ensure proper programming. Gallery See also Programmable ROM EEPROM Flash memory Intel HEX - File format SREC - File format Programmer (hardware) Notes References Bibliography External links Intel EPROM datasheets - intel-vintage.info 1976 Intel Data Book, includes 1702, 2704, 2708 datasheets - archive.org Detailed information about EPROM types and EPROM programming Video of the Intel 1702 EPROM Non-volatile memory Integrated circuits Computer memory