how to latch 7 segment display( 3 digit)

Discussion in 'Homework Help' started by soohino, Jan 15, 2005.

  1. soohino

    Thread Starter New Member

    Jan 15, 2005
    i have a problem here. if i wanted to use one port of microcontroller to show 3 digit (with 2 decimal points) say, the data would be from 0.00V till 5.00 V. so how can i latch my 7 segment display?? how to connect the latch?is it one 7 segment display needs a latch IC? then what else to be considered when writing assembly language if i using latch??

    Anyone can help me?urgent
  2. pebe

    AAC Fanatic!

    Oct 11, 2004
    You need 3 latches (1 for each display) and a latch selector chip. You will need 1 port (8 bits) to send the 7 segment data to all the latch inputs together. While the data is on the port, you need to select which latch you are writing to, and capture the data. That will take a further 3 bits of another port.

    Write to each latch, in turn. You will then have 7segment data + decimal points for all the displays available together. If you want, I have software based on the ST62 series with a description available. I can send if you give me a few days and your email address.

    Alternatively, you could multiplex the segments and drive each digit in sequence from an 8bit port. But assuming each segment needs 10mA then each bit of the port would need to handle 30mA. The displays could be selected with 3 further bits of another port driving 3 transistors - each capable of providing 80mA.
  3. beenthere

    Retired Moderator

    Apr 20, 2004

    You can use 3 up/down counters with parallel outputs. One line from the micro clocks, another gives the up/down level. An additional flip-flop can be toggled for the desired decimal point enable. That way you only have to change the display when the data changes - no multiplexing overhead, plus you free up other port outputs for other purposes.