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Assignment 5: Memory-Mapped Address Decoding
Your combo logic circuit should generate a true signal (0 output) when all of these conditions are satisfied, and a false signal (1 output) otherwise.
Wire your circuits output to the clock input of HC574 latch chip as illustrated. Connect the HC11 PORTC data bus to the inputs of the HC574. Wire the latchs outputs to LEDs. Make sure to wire the latchs pin 1 output control enable to ground!
The test program expanddemo.s is provided to help you test your design. When bootloaded into the HC11, the code puts the HC11 into expanded mode (enabling the address bus, data bus, and R/~W signals), and then writes sequential numbers 0, 1, 2, etc. to address 0x5000. In between each memory write, the piezo line is toggled, producing a click. There is about a half-second pause between each memory write/piezo click.
When you attempt to bring up your circuit, make sure you have Port A 4 (pin 4 of the HC11) connected to the piezo! You should then hear a continuous click...click...click... while the expanddemo.s program is running. Make sure you hear the clicking! If you dont, the program isnt running and your design has no chance of working!
Lets take a look at the expanddemo.s program:
;;; expanddemo.s ;;; puts HC11 in expanded mode, ;;; writes sequentially increasing values to address 0x5000, ;;; and delays and clicks on PA4 between each write ;;; Fred G. Martin / UML CS 2002 PORTA= 0x1000 HPRIO= 0x103c ; highest priority bit int and misc reg ldaa HPRIO ; read the reg oraa #0x20 ; set MDA bit -> expanded mode staa HPRIO ; write it back clrb ; init b at 0 loop: stab 0x5000 ; write b to target incb ; inc it for next time ldaa PORTA eora #0x10 ; toggle piezo bit (click) staa PORTA ldy #0 ; delay for 65k loops delay: dey bne delay bra loop ; againAfter the definitions of the PORTA and HPRIO registers, the first three lines of code set the MDA bit (bit 5) in the HPRIO register. This puts the HC11 into expanded mode. From this point forward, and memory accesses outside of either the internal RAM (0x0000 to 0x01FF) or the register bank (0x1000 to 0x103F) are accomplished using PORTB, PORTC, the R/~W line, and the address strobe (AS) signals.
Next, accumulator B is used as a counter, and is cleared to zero to begin. The core of the program follows. Accumulator B is written to address 0x5000. This causes an external memory access using the HC11 lines just mentioned. Accumulator B is incremented for next time.
Next the piezo line is toggled, causing a click. This is done by loading the A accumulator from PORTA, exclusive-ORing the piezo pin, and storing back.
Next, a long delay loop (about a 1/2 second) is executed using register Y as a 16-bit counter down from 0 and back again.
This process repeats ad infinitum.
To Turn In:
1. Draw a schematic diagram of your circuit that decodes the address from the HC11. Make sure your schematic includes:
2. Also include a brief written explanation of your circuit.
3. After your circuit is working, download the file mystery5000.rel to your HC11. Describe the pattern of lights that you see when running this file.
Last modified: Friday, 18-Oct-2002 22:44:43 EDT by