EE 308
Homework #8
Due March 30, 1998

1. Write a header file pia.h which allows you to refer, for example, to PIA_CRA rather than address 0xB001.
2. Write some C code to set up your 6821 Port B in the following manner:
   • Bits 0-3 of Port B should be outputs, bits 4-8 of Port B should be inputs.
   • An interrupt should be generated on the rising edge of CB1.
   • CB2 should be an input, and An interrupt should be generated on the falling edge of CB2.
3. Write some C code to set up your 6821 pin CA2 to be a general purpose output.
   • Write a line of C code to make CA2 high.
   • Write a line of C code to make CA2 low.
4. Write the master program to implement Lab 10. This program needs to be typed. Be sure to do the following:
   • Set up PIA Port A as an input. Program the PIA so an interrupt is generated on the falling edge of CA1.
   • Set up PIA Port B as an output. Program the PIA so that CB2 is an output, no interrupt is generated on CB1, and CB2 operates in the pulse handshaking mode.
   • Write an interrupt service routine which will be executed when the button is pushed. In this ISR you should read PIA Port A, send the data to PIA Port B, and wait until an acknowledgement is received from the slave.

5. Write the slave program to implement Lab 10. This program needs to be typed. Be sure to do the following:
   • Set up PIA Port A as an input. Program the PIA so an interrupt is generated on the falling edge of CA1, CA2 is an output, and CA2 operates in the pulse handshaking mode.
   • Set up PIA Port B as an output.
   • Define four global variables each of which will hold the value for one of the four patterns (in the case of the T-Bird, it will hold the index value of the T-Bird table). Initialize these to 0.
   • Define a global array for the T-Bird table. Declare the array to be on type const, and initialize it when your define it.
   • Define a global variable which will hold the pattern to implement on the LEDs. Initialize this to 0.
   • In your IRQ interrupt service routine, update the pattern global variable (described above) to indicate which pattern to display. Also in this ISR, change the update rate as told by the master.
   • In your RTI interrupt service routine, look at the pattern global variable to determine which pattern to display, and update the global variable for that pattern.
   • Make sure you do not remain in either of the interrupt service routines for very long. Neither of the routines should use while, for or do loops.

6. Look at the 6821 data sheet. Determine the values of the times described in Part 5 of Lab 10 (except for (a)).

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Bill Rison, <rison@ee.nmt.edu >