Differences

This shows you the differences between two versions of the page.

--- en:multiasm:exercisesbook:avr:sut:scenarios:avr3 [2026/05/03 19:59] – created pczekalski
+++ en:multiasm:exercisesbook:avr:sut:scenarios:avr3 [2026/05/12 10:01] (current) – pczekalski
@@ Line 1: / Line 1: @@
+====== AVR3: Using 7-segment display ======
+In this scenario, you will implement a code that displays on the 7-segment display.\\
+** Prerequisites **\\
+You need to book one of the AVR laboratory nodes and ensure the video stream is live.
+** Scenario **\\
+Implement an algorithm that displays your birth year (or any other 4-digit number) on the LED 7-segment display.
+** Result **\\
+Observe the number via the video stream.
+** Start **\\
+Use AVR GCC syntax (as in the instruction): node compilation facilities are preconfigured, and you do not need to build a Makefile; still, it is necessary to follow the exact AVR GCC syntax, e.g., in the case of ''.equ''.\\
+Use the function ''display_digit'' that handles displaying a single digit, as provided in the [[..:..:sut|]] to bootstrap your code.
+Also note you need to define a stack to use ''delay'' separately (if you use ''rcall'' and ''ret'' instructions). It is obligatory.
+In this algorithm, you go "full throttle". You should implement a loop that displays four consecutive digits. At 16 MHz, shield latches responsible for handling the display are close to their limits but still operate fine. Naturally, in a real-world scenario, you would not waste energy implementing it this way. Would you?
+** Step 1 **\\
+Compose application definitions and configuration. Set up a stack. We do not use the'.section' directive here, but if you plan to use RAM, '.sections' are required and simplify your code.
+<code asm>
+; --- Single .equ for RAM End ---
+.equ SPH,      0x3E     ; Stack Pointer High
+.equ SPL,      0x3D     ; Stack Pointer Low
+.equ SER_PORT, 0x05     ; PORTB I/O address
+.equ SER_PIN,  0        ; GPIO8
+.equ DDRD,     0x0A     ; Data Direction Port D
+.equ DDRB,     0x04     ; Data Direction Port B
+.equ CLK_PORT, 0x0B     ; PORTD I/O address
+.equ CLK_PIN,  7        ; GPIO7
+.equ LAT_PORT, 0x0B     ; PORTD I/O address
+.equ LAT_PIN,  4        ; GPIO4
+.equ RAMEND,   0x08FF   ; Arduino Uno memory size
+.section .text
+.org 0x0000
+    rjmp RESET
+reset:
+    ; Initialise Stack Pointer using hi8 and lo8 functions
+    ldi r16, lo8(RAM_END)
+    out SPL, r16
+    ldi r16, hi8(RAM_END)
+    out SPH, r16
+</code>
+** Step 2 **\\
+Configure pins that control the display as outputs (GPIO 8, GPIO 7, GPIO 4):
+<code asm>
+    ; Initialise display control outputs
+    sbi DDRB, SER_PIN  ; Set PB0 as output
+    sbi DDRD, CLK_PIN  ; Set PD7 as output
+    sbi DDRD, LAT_PIN  ; Set PD4 as output
+</code>
+** Step 3 **\\
+Make a loop that calls the 'display_digit' function four times, varying the numbers and positions. Load arguments.
+As you use constant variables (the easiest, naturally, use ''ldi'' to load registers. Note that digit indexes are zero-based; thus, the leftmost digit is at position 0, and the rightmost is at position 3.
+**Step4**
+Copy ''display_digit'' function from the manual to your code and put it after the end of your main loop.
+<code asm>
+main_loop:
+    ; Display Pattern A (D2, D4 ON)
+    ldi r16, PATTERN_A
+    out PORTB, r16
+    rcall delay_2s
+    ; Display Pattern B (D1, D3 ON)
+    ldi r16, PATTERN_B
+    out PORTB, r16
+    rcall delay_2s
+    rjmp main_loop
+</code>
+** Result validation **\\
+You should be able to see the number on the 7-segment display via the video stream.
+** FAQ **\\
+When using the printed version of this manual, please refer to the latest online version for the most up-to-date list of FAQs.\\
+**It does not show up at all**: Did you compile and upload to the device? Those are separate steps: it is not enough to just compile, but you also need to "flash" the MCU. Also, check your video stream if it "ticks" - the time embedded into the video stream should change. Your code may be working OK, but the video stream can be frozen, so you cannot see it working properly!
+//

en/multiasm/exercisesbook/avr/sut/scenarios/avr3.txt · Last modified: 2026/05/12 10:01 by pczekalski