UPC EETAC Bachelor's Degree in Telecommunications Systems and in Network Engineering EEL

Chapter 2 problems

- B3.7 -

Multiplexed displays: A: 7-segment

B: LED bar

Products

B3.6

B3.8

1. Specifications

Because microcontrollers typically have a limited number of pins, implementing a multiplexed display system (MDS) is an effective way to reduce the required pin count when multiple displays are needed. Review the MDS tutorial for more details. For instance, a 10-digit calculator display requires only 17 pins to display any number from 0000000000 to 9999999999, with the Binary-Coded Decimal (BCD) data stored in 10 bytes of RAM.

The same project is proposed in D1.7 as a combinational circuit based on logic gates.

We can design the BCD_7seg_MUX_3digit represented in Fig. 1. To practise with polling inputs, we will imagine that the H, T and U data is external, generated by 12 switches. Select signal S(1..0) can be generated externally for example at 1 kHz by a modulo 3 counter, S = 0, 1, 2, 0, 1, 2, 0, ... and will multiplex the numbers to the corresponding displays.

- When S = 0, CA_L = "110" and the number U is decoded at segment outputs to be represented on digit 0.

- When S = 1, CA_L = "101" and the number T is decoded at segment outputs to be represented on digit 1.

- When S = 2, CA_L = "011" and the number H is decoded at segment outputs to be represented on digit 2.

 

Symbol and application

Fig. 1. Symbol for this MDS_HEX_7seg_3digit and the external driving circuit for the common anodes. Only one digit is activated at a time.

A) Planning hardware

Pin assignment option #1:

H(3..2) ---> RD(7..6) H(1..0) ---> RC(1..0)
T(3..2) ---> RD(5..4) T(1..0) ---> RC(3..2)  
U(3..2) ---> RD(3..2) U(1..0) ---> RC(5..4)  
S(1..0) ---> RD(1..0)    
CA_L(2..0) ---> RB(7..5)  
a_L, b_L, c_L, d_L ---> RB(4..1) e_L, f_L, g_L ---> RA(3..1)  

 

Pin assignment option #2:

H(3..2) ---> RA(5..4) H(1..0) ---> RB(7..6)
T(3..2) ---> RB(5..4) T(1..0) ---> RD(7..6)  
U(3..1) ---> RD(5..3) U(0) ---> RC(7)  
S(1..0) ---> RC(6..5)    
CA_L(2..0) ---> RC(4..2)  
a_L, b_L ---> RC(1..0) c_L, d_L, e_L, f_L ---> RA(3..0) g_L ---> RB(2)

 

Pin assignment option #3:

H(3..1) ---> RC(7..5) H(0) ---> RD(7)
T(3..0) ---> RD(6..3)    
U(3..2) ---> RB(7..6) U(1..0) ---> RA(5..4)  
S(1..0) ---> RA(3..2)    
CA_L(2..0) ---> RB(5..3)  
a_L, b_L, c_L ---> RD(2..0) d_L, e_L, f_L, g_L ---> RC(4..1)  

 

Project location:

 C:\CSD\P9\MDS_BCD_7seg_3digit\(files)

 

Chapter 2 problems

- B3.7 -

Multiplexed displays: A: 7-segment

B: LED bar

Products

B3.6

B3.8

1. Specifications

In this project we propose to use a µC PIC18F48K22 to implement the combinational circuit Bar_28LED_dec represented in Fig. 1. The same project is proposed in D1.7 as a combinational circuit based on logic gates (complete and use the truth table in Fig. 7).

Symbol for the Bar_28LED_dec

Fig. 1. Symbol of the Bar_28LED_dec.

A) Planning hardware

 To practise with polling inputs we will imagine a hardware circuit in Proteus where number B and enable E are generated by 6 switches. You can also use the schematic "Hex_7seg_MUX_2digit.pdsprj" to drive le LED bar and check results.

Pin assignment option #1:

B(4..3) ---> RD(7..6) B(2..0) ---> RC(5..3)
E ---> RE(1)  
A_L(3..2) ---> RB(7..6) A_L(1..0) ---> RC(7..6)
K(6..5) ---> RA(3..2) K(4..3) ---> RB(4..3) K(2..0) ---> RD(3..1)

 

Pin assignment option #2:

B(4..3) ---> RC(5..4) B(2..0) ---> RD(7..5)
E ---> RB(1)  
A_L(3..2) ---> RA(3..2) A_L(1..0) ---> RB(6..5)
K(6..5) ---> RC(7..6) K(4..3) ---> RD(4..3) K(2..0) ---> RE(2..0)

 

Pin assignment option #3:

B(4..3) ---> RE(2..1) B(2..0) ---> RA(3..1)
E ---> RD(7)  
A_L(3..2) ---> RB(1..0) A_L(1..0) ---> RC(7..6)
K(6..5) ---> RB(5..4) K(4..3) ---> RC(1..0) K(2..0) ---> RD(5..3)

 

Project location:

 C:\CSD\P9\Bar_LED28_dec\(files)

 

NOTE (optional): This project can be continued using the software implementation of FSM proposed in P10 to complete the the full Bar_28LED.