ssozonoff wrote:I need to hook the GPS module up to a data logger which uses 5v TTL logic.
This GPS module uses 2.8v CMOS level logic. I am not sure what the max min voltage levels are for standard TTL to register the high and low states so the question is will hooking up the GPS module to a TTL level input work or not.
If no, what sort of a chip or circuit do I need to shift the logic level from 2.8v to 5v?
Sorry for the beginner question.
Thanks,
Serge
I'm not positive on this, but I believe all PICs are tolerant of 2.8v CMOS logic INPUT. I am positive that the 18F452 is. It's best to chek the datasheet on both the GPS and the logger's microcontroller to see what the maximum voltage for a low output/input is, and what the minimum voltage for a high output/input is. However, I'm pretty sure that it's CMOS logic that's quite succeptible to latch-up problems, and wouldn't be tolerant to any input beyond it's maximum rating - usually something like 3.3V.
The easiest way to translate logic between two voltage levels is to use a non-inverting hex buffer, feed its input with the higher voltage output, power it at the lower voltage's typical maximum, and feed its output into the lower logic level's input. In most cases, you should be able to get away with feeding the output from the 2.8v CMOS directly into the 5v input, but I'm pretty sure that only works if the inputs are high-impedance inputs.
