1 files changed, 36 insertions, 0 deletions
diff --git a/PIC/test_uart.c b/PIC/test_uart.c
new file mode 100644
index 0000000..f453e21
--- /dev/null
+++ b/PIC/test_uart.c
@@ -0,0 +1,36 @@
+#include <pic16f84a.h>
+
+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 void uart_send(uint8_t byte) {
+    while (UART_STATUS & 0x01);    // wait until tx_busy = 0
+    UART_TX = byte;
+}
+
+static void uart_puts(const char *s) {
+    while (*s) {
+        uart_send((uint8_t)*s);
+        s++;
+    }
+}
+
+void main(void) {
+    uart_puts("Hello from PIC!\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);
+        }
+    }
+}