Advanced Peripheral LCD_DISPLAY_4DIGIT does not work or I don't understand it.

[Gunner659]

I am trying to develop a lab using the Advanced Peripheral LCD_DISPLAY_4DIGIT. 

I have worked out the pinout for the segments, and I assume pin 1 is the backplane.  I have made sure that the segments are getting a TTL squarewave which is either in-phase or 180 degrees out-of-phase with the backplane.  However, while simulating, all the digit does is flash.  When I turn the sim off, the desired digit usually shows, but not always.  The device info window says the minimum frequency of the backplane is 32 hz (I assume that it means minimum frequency) and I have tried backplane frequencies from there all the way up 32K.  It still just flashes at me.

I have simplified the circuit down to a single xor gate with a switch on one input and the backplane on the other driving a single segment with the same results.

[Tien_P]

Hi,

I connected a 32 Hz clock to pin 1 and the display not flashing for me, looks like the part is an active low.

[Gunner659]

I am attaching my Multisim 13 circuit.  A bit more on the complicated side then what you showed.  It worked correctly in version 12 but flashes with 13. 

The comment about the possibility that it is an active low device is interesting.  If so, I shouldn't need the inverter that is inverting the backplane due to the 7447 active low outputs.  However, I don't see one way or the other.  I am pretty sure I had to use the inverter in version 12.

[Gunner659]

This reply is significantly late, but here it is.

The LCD has to have a square wave on the backplane and a squarewave on each segment to work. Either in phase or out of phase determines if segment is on or off.  Your circuit has a square wave on backplane but DC voltages on the segments.  The circuit flashes as long as there are squarewaves on both backplane and segments.