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

Chapter 3 problems

      - B3.13 -

8-bit subtractor (μC - C)

Products

B3.12

B3.14

1. Specifications

As a way to start using the new developing environment (IDE) and to discover the main details of microcontroller architecture and how to program it, we can try to solve in C for a target chip PIC18F46K22 several components belonging to the 8-bit subtractor proposed in D1.13 and reproduced in Fig. 1 along with its internal circuit in Fig. 2. 

Subtractor symbol

Fig. 1. The entity of a Subtractor_8bit and an example operation.

Planning schematic

Fig. 2. Fully-annotated architecture for the full Subtractor_8bit ready for VHDL translation in D1.13.

 

Project #1 Chip1 + Chip2: Subt_8bit + Sign_corrector. This combination may be named Subt_radix2_8bit as represented in Fig. 3.

Symbol

Fig. 3. Symbol of the Subt_radix2_8bit.

Pin assignment option #1:

M(7..4) ---> RA(5..2) M(3..0) ---> RB(7..4)  
S(7..6) ---> RA(1..0) S(5..2) ---> RB(3..0) S(1..0) ---> RC(7..6)
D(7..2) ---> RC(5..0) D(1..0) ---> RD(7..6)  
N ---> RE(2)    

 Pin assignment option #2:

M(7..5) ---> RD(5..3) M(4..1) ---> RC(7..4) M(0) ---> RA(0)
S(7..5) ---> RD(2..0) S(4..0) ---> RB(7..3)                      
D(7..5) ---> RE(3..1) D(4..0) ---> RA(5..1)  
N ---> RD(7)    

Pin assignment option #3:

M(7..4) ---> RC(5..2) M(3..0) ---> RB(7..4)                      
S(7..6) ---> RB(3..2) S(5..0) ---> RA(5..0)  
D(7..6) ---> RC(1..0) D(5..0) ---> RD(7..2)  
N ---> RD(0)    

 

Project #2 Chip3: BCD_bin_3digit  [B3.15]. Pin options are given in this related assignment.

Symbol and truth table

Fig. 4. Symbol for the BCD_bin_3digit code converter.

 

Project #3 Chip5: Bin_BCD_9bit [B3.16] (let us add another bit to the binary input). Pin options are given in this related assignment.

Symbol

Fig. 5. Symbol for the Bin_BCD_9bit code converter.

 

Project #4 Chip6 - Chip7 - Chip8: the three of them integrated in a single 3-digit multiplexed hexadecimal to 7-segments decoder. Similar tutorial on multiplexed display systems at  MDS. Pin options and details are given in this related assignment [B3.7].

Microcontrollers do not have many pins, thus it is convenient to generate a multiplexed display system (MDS) to reduce the pin count when several displays are required in a given application, for instance this MDS_BCD_7seg_3digit.

Symbol and application

Fig. 6. Symbol for this MDS_HEX_7seg_3digit.