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Two Line Alphanumeric (moving) Display


The 8255 digital I/O card is programmable peripheral interface chip, which is used with microprocessor. This programmable peripheral interface (PPI) is an adaptable and convenient to create circuit card the plugs into an existing slot in PC (Rafiquzzaman, 2005). This programmable peripheral interface is considered resourceful and handy for input/ output chip that can easily be set to perform in different programs. Thus, using 8255 programmable peripheral interface improves the I/O lines of microcontroller (El-Abiad, 2006). Considering the significance of this I/O card, this paper aims to create two lines alphanumeric (moving) display using the data sheet for the two lines x16 characters LCD display module. Additionally, there is to create an interface of module to the 8255 digital I/O card together with C program such that a predetermined message scrolls on the LCD Display. The PCI bus 8255 adapter enables to use the 6 digital I/O ports, while each port carrying 8 I/O lines providing a total of 48 digital I/O lines. It also gives a highest of 10MHz count rate and programmable I/O control functions. Professional assignment help online.


Block Diagram

  • In the above block diagram, D0-D7 are the data input and output lines, which are used for the device. The information read and written to the 8255 takes place through 8 data lines.
  • If Chip Select Input (CS) line is a logical 0, then the microprocessor will be able to read and write to the8255
  • If read Input line (RD) is a logical 0 along with the RD input a logical 0, the 8255 data outputs will be enabled against the system data bus
  • If write input (WR) line is a logical 0 along with CS input a logical 0, then data is written to the 8255 using the system data bus
  • A0 - A1 are the address inputs, where the logical grouping of these two input lines decides internal register of the 8255 data to be written to or read from.
  • The 8255 is put into the RESET, and if this input line seems to be a logical 1. All the peripheral ports are created to the input mode.
  • PA0 - PA7, PB0 - PB7, PC0 - PC7 are signal lines, which are used as 8-bit I/O ports. These signal lines may be interlinked to peripheral devices. The 8255 possesses three 8 bit I/O ports and every port may be connected to the physical lines of the external device. Moreover, these lines are tagged as PA0-PA7, PB0-PB7, and PC0-PC7. The combination of the signals is further classified into three numbers of I/O ports tagged port A (PA), port B (PB), and port C (PC) (Park & MacKay, 2003) 

Flow Chart

The flow chart demonstrates the process through which user can input to view the programming graphs.


int i;

int length= strlen(originalString);


for (i= 0; i< length; ++i)




    if (!(isalpha(originalString[i])))


        puts('Please Enter alphanumeric message.');






Conclusion and Recommendation

This paper was aimed at creating two lines alphanumeric (moving) display using the data sheet for the 2 line x16 characters LCD Display module together with interface the module to the 8255 digital I/O card. This paper presented the block diagram that elaborates and explains the intersection of all system. Based on the programming generated using 8255 digital I/O card, certain level of lacking has been identified, which is likely to limit the scope of the project including limited user input and lack of user friendliness. Based on the project limitation, future recommendation can be made to improve the system by incorporating new commands and enhancing the user friendliness options.

It is recommended for future research that users can decide which form of movement of alphanumeric letter they want to perform for example for scrolling user is required to enter s,for pulse movement p will be press, for clock movement c will be press. For different symbols rectangle or triangle r and t is used. User can also implement the movement of the alphanumeric key using different I/O card besides 8255. The user can change the colors of the alphanumeric characters with the requirement of the user.


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