I'm trying to create a simple circuit that would allow me to select which micro (w77e58 or at89C52) to program using jumpers and data input. Based on datasheets, the w77e58 use P3.0 through P3.3 to determine what programming operation happens. at89C52 does not.
The w77e58 also uses P3.0 to determine whether erase mode should be active or not while P3.1 through P3.3 should be logic low.
In the circuit, P3.0 through P3.3 are the top 4 connections on the microcontroller side and all have reverse-based diodes and pull-up resistors.
I use reverse based diodes because I only want high impedance input to those pins if the at89C52 is used (I don't think high impedance will destroy the chip?), but if the other chip is used then I want P3.0 controllable and P1.3 to P3.3 logic low.
In the schematic, DEV means device. If DEV = high then its a w77e58 device we want. Otherwise its at89C52. Feature is the actual erase option that controls P3.0
So if this schematic is OK to use, then for diodes, could I get away with 1N914/1N4148? and for resistors, could I get away with 100K or is that too high for either microcontroller to see as a logic high?
The w77e58 also uses P3.0 to determine whether erase mode should be active or not while P3.1 through P3.3 should be logic low.
In the circuit, P3.0 through P3.3 are the top 4 connections on the microcontroller side and all have reverse-based diodes and pull-up resistors.
I use reverse based diodes because I only want high impedance input to those pins if the at89C52 is used (I don't think high impedance will destroy the chip?), but if the other chip is used then I want P3.0 controllable and P1.3 to P3.3 logic low.
In the schematic, DEV means device. If DEV = high then its a w77e58 device we want. Otherwise its at89C52. Feature is the actual erase option that controls P3.0
So if this schematic is OK to use, then for diodes, could I get away with 1N914/1N4148? and for resistors, could I get away with 100K or is that too high for either microcontroller to see as a logic high?