diff --git a/doc/specifications/86box-unit-tester.md b/doc/specifications/86box-unit-tester.md
index 77279a3ee..9100f59de 100644
--- a/doc/specifications/86box-unit-tester.md
+++ b/doc/specifications/86box-unit-tester.md
@@ -95,8 +95,6 @@ This is how most commands will work.
 
 ### 0x00: No-op
 
-**TODO: IMPLEMENT ME!**
-
 This does nothing, takes no input, and gives no output.
 
 This is an easy way to reset the status to 0x04 (no command in flight, not waiting for reads or writes, and no errors).
diff --git a/src/device/unittester.c b/src/device/unittester.c
index ff605e119..e6deb45bc 100644
--- a/src/device/unittester.c
+++ b/src/device/unittester.c
@@ -39,6 +39,20 @@ enum fsm2_value {
     UT_FSM2_WAIT_IOBASE_1,
 };
 
+/* Status bit mask */
+#define UT_STATUS_AWAITING_READ   (1<<0)
+#define UT_STATUS_AWAITING_WRITE  (1<<1)
+#define UT_STATUS_IDLE            (1<<2)
+#define UT_STATUS_UNSUPPORTED_CMD (1<<3)
+
+/* Command list */
+enum unittester_cmd {
+    UT_CMD_NOOP = 0x00,
+    UT_CMD_CAPTURE_SCREEN_SNAPSHOT = 0x01,
+    UT_CMD_READ_SCREEN_SNAPSHOT_RECTANGLE = 0x02,
+    UT_CMD_VERIFY_SCREEN_SNAPSHOT_RECTANGLE = 0x03,
+};
+
 struct unittester_state {
     /* I/O port settings */
     uint16_t trigger_port;
@@ -50,6 +64,10 @@ struct unittester_state {
     /* FSM2: IOBASE port selection, once trigger is activated */
     enum fsm2_value fsm2;
     uint16_t        fsm2_new_iobase;
+
+    /* Runtime state */
+    uint8_t             status;
+    enum unittester_cmd cmd_id;
 };
 static struct unittester_state unittester;
 static const struct unittester_state unittester_defaults = {
@@ -57,6 +75,7 @@ static const struct unittester_state unittester_defaults = {
     .iobase_port  = 0xFFFF,
     .fsm1         = UT_FSM1_WAIT_8,
     .fsm2         = UT_FSM2_IDLE,
+    .status       = UT_STATUS_IDLE,
 };
 
 /* FIXME TEMPORARY --GM */
@@ -85,8 +104,22 @@ unittester_write(uint16_t port, uint8_t val, UNUSED(void *priv))
 {
     if (port == unittester.iobase_port+0x00) {
         /* Command port */
-        /* TODO! --GM */
         unittester_log("[UT] W %02X Command\n", val);
+
+        switch (val) {
+            /* 0x00: No-op */
+            case UT_CMD_NOOP:
+                unittester.cmd_id = UT_CMD_NOOP;
+                unittester.status = UT_STATUS_IDLE;
+                break;
+
+            /* Unsupported command - terminate here */
+            default:
+                unittester.cmd_id = UT_CMD_NOOP;
+                unittester.status = UT_STATUS_IDLE | UT_STATUS_UNSUPPORTED_CMD;
+                break;
+        }
+
     } else if (port == unittester.iobase_port+0x01) {
         /* Data port */
         /* TODO! --GM */
@@ -101,14 +134,13 @@ unittester_read(uint16_t port, UNUSED(void *priv))
 {
     if (port == unittester.iobase_port+0x00) {
         /* Status port */
-        /* TODO! --GM */
-        unittester_log("[UT] R -- Status\n");
-        return 0x04;
+        unittester_log("[UT] R -- Status = %02X\n", unittester.status);
+        return unittester.status;
     } else if (port == unittester.iobase_port+0x01) {
         /* Data port */
-        /* TODO! --GM */
         unittester_log("[UT] R -- Data\n");
-        return 0xFE;
+        /* TODO! --GM */
+        return 0xFF;
     } else {
         /* Not handled here - possibly open bus! */
         return 0xFF;