hi i am doing a project where i have to read a 2 byte hex code from a Card reader , in an external ROM create a table with every code corresponding to a num , once the code is read extract the corresponding num and display it . i am using 8255 and using 2 of its ports to read the code and one port to connect to a display unit having 5 seven segment displays . is this the most efficient way for this application . i am a amature in this field and am finding the programming part a bit difficult
It sounds to me that for this application, the ROM is a fixed lookup table. It could be anything from a pre-programmed flash or EEPROM to OTP to a mask ROM. The method of programming would really depend on their manufacturing environment and volumes. The bar code readers I'm familiar with use a serial interface rather than a parallel one, and would be connected to an 8051 UART (SPI, I2C, etc). You haven't mentioned exactly what the device is, so perhaps a parallel interface is appropriate. Similarly for your numerical display; without part numbers, we can't really know what the interface is. Selecting an appropriate 8051 variant would give you the I/O ports built into the microcontroller. The external ROM will kill P0/P2 on many variants, which still leaves P1/P3. If the interface to the reader or display could be serial, then you can eliminate the 8255 from the board. (The point of a microcontroller is to eliminate the glue logic and components, after all.)