On Tue, May 19, 2015 at 6:20 PM, Richard B. Main, Esq. <mainpatents at gmail.com> wrote: It may "sound wrong", but that's actually the *only* way to read the EPROM 8741, 8741A, 8748, and 8749. If you don't apply high voltage to the EA pin, it doesn't go into verify mode. It's fully documented in the data sheet, and I've verified that commercial programmers do that. It's possible that verification will work at somewhat less than 25V, but it definitely does NOT work at under 6V. The issue is that the 8041, 8041A, 8048, and 8049 masked-ROM parts are not rated for 25V on EA. The 8748 and 8749 datasheets say to use 12V on EA. The 8041 and 8041A datasheets don't say, but since it's almost the same design and definitely the same fab process as the 8048, I'm pretty sure that they need 12V also.

from the outside; also I must have misremembered

On Tue, May 19, 2015 at 11:28 PM, Mike Stein <mhs.stein at gmail.com> wrote: "Normal operation" is the key phrase. ROM (or EPROM) verification mode is not considered "normal operation". In normal operation, the 8041A/8641A/8741A is executing the ROM/EPROM code, and you can apply an address externally to the port pins until the cows come home, but that won't make it dump the contents of that address. This isn't a 2716. There isn't a "read (normal)" mode. Normal mode is executing code, and doesn't allow reading the ROM (or EPROM) contents externally. Verification mode is the only mode that provides for external access to the ROM/EPROM contents. The only documented way the chip knows to be in verification mode is a supervoltage on the EA pin. A National Semiconductor app note suggests that 9V is adequate for reading their 804x masked ROM parts; they specifically mention internal circuitry that detects a voltage on EA above a certain threshold which puts the part into verification mode. The 9V National describes might or might not be adequate to read Intel masked ROM parts. Intel specified 12V to read the 8048. Intel neglected to specify the supervoltage required for ROM verification mode for the 8041 and 8041A, but I'm pretty sure they expected 12V for those as well.