AT89C2051 programmer

[Md Mubdiul Hasan]

Hi,

Even its 1950's project, I feel interest on it. You might feel it silly!
I am trying to get attraction those people, who knows its hardware well.

Its a serial interface project, someone who posted it online.
Take a look this schematic, I have few questions.


1. Does the  resistors R1 and R2 has connection with PIN4 of  DM7406? Did you see those are connected with regulator input?
2. Whats the reason of invert signals by buffer here?
3. Does the pull-up resistors are on matched value against IN/OUT current and voltage ? I got MAX and MIN pull-up resistor value setting equation on DM7406.
4. Anything wrong you could see in this design?

Kindly post your comment here.