fix operand order of subtraction. add rollover counter UART test.

1 files changed, 43 insertions, 12 deletions

diff --git a/PIC/test_uart.c b/PIC/test_uart.c
index f453e21..2656371 100644
--- a/PIC/test_uart.c
+++ b/PIC/test_uart.c
@@ -2,22 +2,32 @@
 
 typedef unsigned char uint8_t;
 
-// UART memory-mapped registers (hooked up in dpram.vhd).
-// Placed at 0x70-0x72: unimplemented in the real PIC16F84A so no
-// conflict with the SFR definitions in pic16f84a.h.
-//   0x70  UART_TX     write: transmit a byte
-//   0x71  UART_RX     read:  receive a byte (pops the RX FIFO)
-//   0x72  UART_STATUS read:  bit0=tx_busy, bit1=rx_empty, bit2=rx_full
 __sfr __at(0x70) UART_TX;
 __sfr __at(0x71) UART_RX;
 __sfr __at(0x72) UART_STATUS;
 
+static volatile uint8_t _d0, _d1, _d2;
+static uint8_t counter;
+
+static void delay(void) {
+    _d0 = 0;
+    do {
+        _d1 = 0;
+        do {
+            _d2 = 0;
+            do { _d2++; } while (_d2 != 0);
+        } while (++_d1 != 30);
+        _d0++;
+    } while (_d0 != 116);
+}
+
 static void uart_send(uint8_t byte) {
-    while (UART_STATUS & 0x01);    // wait until tx_busy = 0
+    while (UART_STATUS & 0x01); 
     UART_TX = byte;
 }
 
-static void uart_puts(const char *s) {
+// Keep this ONLY for literal strings (ROM)
+static void uart_puts_rom(const char *s) {
     while (*s) {
         uart_send((uint8_t)*s);
         s++;
@@ -25,12 +35,33 @@ static void uart_puts(const char *s) {
 }
 
 void main(void) {
-    uart_puts("Hello from PIC!\r\n");
+    counter = 0;
+    uart_puts_rom("Hello\r\n");
 
-    // Echo loop: read every incoming byte and send it back
     while (1) {
-        if (!(UART_STATUS & 0x02)) {    // rx_empty = 0 → data available
-            uart_send(UART_RX);
+        uint8_t v = counter;
+        uint8_t started = 0;
+
+        uart_send('C');
+        uart_send(':');
+
+        // Hundreds
+        if (v >= 200) { uart_send('2'); v -= 200; started = 1; }
+        else if (v >= 100) { uart_send('1'); v -= 100; started = 1; }
+
+        // Tens
+        {
+            uint8_t tens = '0';
+            while (v >= 10) { v -= 10; tens++; }
+            if (started || tens != '0') { uart_send(tens); }
         }
+
+        // Units (always)
+        uart_send(v + '0');
+
+        uart_puts_rom("\r\n");
+
+        counter++;
+        delay();
     }
 }