7 segment LED w/MSP430 and CD74HC273 (serial display).
  5 digits screen (+8 LEDs line) based on two CD74HC273. Simple serial data exchange with MSP430, via 'Data' & 'Clock' lines.

Any questions - e-mail below.
Key - 7LED in subject.

  Whatever the reasons for doing this, below is the display circuit, which shows a 5-digit number. The additional 8 LEDs works like another '7-segment'. Serial data exchange was chosen because it requires only two lines.

  Converting a serial to a parallel occurs in 74HC273 that contains 8 flip-flops with a common clock and reset. The output of each trigger is connected to the input of the next one as you can see in the following.

  This method has one drawback: the MSP430 must update the screen nonstop, upload and light the first digit, then the second, and so on. Considering that it is necessary to touch 6 positions (5 7-segment and one 8 LED line) to protect against screen's flicker, the micro controller must operate at 8 MHz (MCLK).

  Serial coding is simple. The positive edge on a 'clock' line writes status of 'data' line to the first trigger. The next 'clock' pulse, overwrites it to the next trigger and so on. After 16 pulses, all triggers will be updated.

  On the other hand, "0", in this 16 bit sequence, will light 7-segment or LEDs. The first 8 bits - are position, the second 8 bits - are segments, or LEDs.  For example

   11111111 11111111 (0xFFFF) - all 'OFF';
   01111111 10111111 (0x7FBF) - 'dot' in second position from left;
   11111000 01111111 (0xF87F) - '7' in first position;
  11000000 11111011 (0xF0FB) - line of 6 LED, from left, are 'ON'.
   * assuming that you push LSB (Least Significant Bit) first.

  The following two examples of programs allow you to see how it works. The first (test.txt) displays the static word ". tESt" on the screen, the second (time.txt)- the stopwatch, counting with hundredths of a second, which is reset by power cycle. Copy the text to main.c in
CCS (Code Composer Studio) and run it . Will work on any MSP430 from TI.

  What to show on the screen is a matter of fantasy and necessity. The important thing is that it's simple, and does not take much time for coding.

Nov.18,2017  SK_Lab


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