diff --git a/src/gpio.zig b/src/gpio.zig
index a17df27..588a350 100644
--- a/src/gpio.zig
+++ b/src/gpio.zig
@@ -1,12 +1,67 @@
 const regs = @import("atmega328p.zig").registers;
 
-/// For now only supports PORTB
-pub fn init(comptime pin: u8, comptime dir: enum { in, out }) void {
+const MODE = enum { in, out };
+
+// PORTB: pins D8 to D13
+fn init_portb(pin: u3, comptime dir: MODE) void {
     regs.PORTB.DDRB.* = @as(u8, @intFromEnum(dir)) << pin;
 }
 
-pub fn toggle(comptime pin: u8) void {
+pub fn toggle_portb(comptime pin: u3) void {
     var val = regs.PORTB.PORTB.*;
     val ^= 1 << pin;
     regs.PORTB.PORTB.* = val;
 }
+
+// PORTD: pins D0 TO D7
+fn init_portd(pin: u3, comptime dir: MODE) void {
+    regs.PORTD.DDRD.* = @as(u8, @intFromEnum(dir)) << pin;
+}
+
+pub fn toggle_portd(comptime pin: u3) void {
+    var val = regs.PORTD.PORTD.*;
+    val ^= 1 << pin;
+    regs.PORTD.PORTD.* = val;
+}
+
+// TODO: PORTC: analog pins
+
+pub const PIN = enum {
+    D0,
+    D1,
+    D2,
+    D3,
+    D4,
+    D5,
+    D6,
+    D7,
+    D8,
+    D9,
+    D10,
+    D11,
+    D12,
+    D13,
+    A0,
+    A1,
+    A3,
+    A4,
+    A5,
+};
+
+pub fn init(comptime pin: PIN, comptime dir: MODE) void {
+    const i = @intFromEnum(pin);
+    if (i <= 7) {
+        init_portd(@as(u3, @intCast(i)), dir);
+    } else if (i >= 8 and i <= 13) {
+        init_portb(@as(u3, @intCast(i - 8)), dir);
+    }
+}
+
+pub fn toggle(comptime pin: PIN) void {
+    const i = comptime @intFromEnum(pin);
+    if (i <= 7) {
+        toggle_portd(@as(u3, @intCast(i)));
+    } else if (i >= 8 and i <= 13) {
+        toggle_portb(@as(u3, @intCast(i - 8)));
+    }
+}
diff --git a/src/main.zig b/src/main.zig
index 7b73e1e..ceabb31 100644
--- a/src/main.zig
+++ b/src/main.zig
@@ -30,7 +30,8 @@ pub fn main() void {
     // var x: u8 = 255;
     // x += 1;
 
-    gpio.init(5, .out);
+    gpio.init(.D13, .out);
+    gpio.init(.D5, .out);
 
     while (true) {
         uart.write_ch(ch);
@@ -41,7 +42,8 @@ pub fn main() void {
             uart.write("\r\n");
         }
 
-        gpio.toggle(5);
+        gpio.toggle(.D13);
+        gpio.toggle(.D5);
         delay_cycles(50000);
     }
 }