On 24/02/2013 17:49, Chris Tofu wrote: Looks like the 8748 is EPROM so it would have a window for UV erasing... Dave

The 8048 with mask ROM is programemd when the IC is made. In fact the ROM contents are determiend my one of the masked used in making the IC. So it's only practical to have that doen if you are buying many thousands of them with the same program in them. The 8748 has an intenral EPROM for the program store. It can be programed 'in the field' using a special EPROM programmer (it's not the same as a noram lEPROM, but the princple is the same). You can program 1-offs. Cerainy some 8748s ahve quartz windows over the die, so you can erase them. The downside is that he data retention time of an EPROM is probaly less than the life of a mask ROM. -tony