NEDSP900 Development Board
13
To NEDSP control Pin
From 3.3v /5v control System
From 3.3v /5v control System
To NEDSP control Pin
a) Transistor (Logic Inversion) Interface 3.3v or 5.5v
c) Resistor Divider Circuit (see values table)
d) Diode Pull Down Circuit
From 3.3v /5v control System
To NEDSP control Pin
To NEDSP control Pin
From 3.3v /5v control System
b) Digital Transistor (Logic Inversion) Interface 3.3v or 5.5v
Circuit a) – This provides a good level conversion interface and has a logic Inversion
function, thus a positive logic from the external system will use the transistor as a switch
that will pull the NEDSP900 control line down.
Circuit b) – There are many types of what are termed Digital Transistors. These are no
more than Circuit a) packaged together in a small surface mount pack. They come in a
variety of input and Base to Emitter resistor values. Again these will perform a logical
inversion.
Circuit c) – This is the simplest circuit and just provides a simple voltage divider action.
Bearing in mind that the NEDSP900 input pins have a maximum of 1.8v voltage limit,
you have to be careful with this. The resistors R3 and R4 need to be changed dependent
on the control logic voltage being used (3.3v or 5v).
There is no logic inversion with this circuit.
Circuit d) - This lets the external control logic pull the NEDSP900 logic down only and
the diode becomes back biased when the external logic goes high, leaving the
NEDSP900 logic to pull up itself. R6 provides a pull down function to give the Diode
something to work against. A value of 100 k Ohms of above is sufficient not to have an
Processor supply R4 Ohms
R3 Ohms
3.3v
1K
820R
5v
1K
1.8K
