diff --git a/code/inventory/scan.c b/code/inventory/scan.c
index 539b12d..8bfa102 100644
--- a/code/inventory/scan.c
+++ b/code/inventory/scan.c
@@ -1,94 +1,58 @@
 /*
  * scan.c - Phase 1 inventory demo: scan UPC barcodes and display them.
  *
- * Opens the barcode serial channel (TTY:D) and its own console/keyboard
- * channel (CON:), then waits on both at once: a completed scan is validated
- * as a UPC-A and printed; pressing Esc quits.
+ * Blocking design: the app opens the barcode serial channel (TTY:D) and reads
+ * it with a blocking p_read, assembling bytes until the scanner's terminator,
+ * then validates and prints each barcode. Exit via the System screen.
  *
- * Asynchronous two-channel wait (PLIB pattern): each request is started with
- * p_ioc, which sets a status word to E_FILE_PENDING until the request
- * completes. p_iowait blocks until some request finishes; we then check each
- * status word, cancel the other outstanding request, and loop. Every started
- * request is matched by exactly one completion (real or cancelled) so the I/O
- * semaphore stays balanced. See "Asynchronous I/O" in the PLIB Reference.
+ * (An earlier version waited on the keyboard asynchronously via CON: so Esc
+ * could quit; that panicked the Window Server - on SIBO the keyboard is
+ * event-driven through the window server, not a raw CON: byte read. A proper
+ * scan-or-key loop needs the Window Server event API, whose reference manual
+ * is not among the SDK docs in this repo. Blocking output via p_printf is
+ * fine, so this version sticks to that.)
+ *
+ * This also serves as the format diagnostic: it prints the byte length of each
+ * decoded barcode alongside the text, so we can see exactly what the scanner
+ * emits for a UPC (12 vs 13 digits, any prefix/suffix) before Phase 2 uses it
+ * as a database key.
  */
 #include <plib.h>
 #include "bcode.h"
 #include "upc.h"
 
-#define KEY_ESC 27
-
-/*
- * If a request on chan is still pending, cancel it and reap the resulting
- * completion, so the started p_ioc is balanced by a wait.
- */
-LOCAL_C VOID cancelPending(VOID *chan, WORD *pStat)
-{
-    if (*pStat == E_FILE_PENDING) {
-        p_iow(chan, P_FCANCEL);
-        p_waitstat(pStat);
-    }
-}
-
 GLDEF_C INT main(VOID)
 {
-    VOID *bchan;                /* barcode serial channel   */
-    VOID *kchan;                /* keyboard console channel */
-    WORD  bStat, kStat;         /* async status words       */
-    UBYTE bRaw[BCODE_MAXLEN];   /* raw bytes from one serial read */
-    UBYTE kRaw[1];              /* one keystroke                  */
-    TEXT  line[BCODE_MAXLEN];   /* barcode assembled across reads */
+    VOID *bchan;
+    UBYTE raw[BCODE_MAXLEN];
+    TEXT  line[BCODE_MAXLEN];
     INT   lineLen = 0;
-    UWORD bLen, kLen;
-    INT   err;
-    INT   quit = 0;
+    INT   err, n, textLen;
 
     if ((err = bcodeOpen(&bchan)) < 0) {
         p_printf("Cannot open barcode port TTY:D (err %d)\n", err);
         return 1;
     }
-    if ((err = p_open(&kchan, "CON:", (UINT)-1)) < 0) {
-        p_printf("Cannot open console (err %d)\n", err);
-        bcodeClose(bchan);
-        return 1;
-    }
 
     p_printf("Inventory scan demo\n");
-    p_printf("Scan a UPC, or press Esc to quit.\n\n");
+    p_printf("Scan UPC barcodes. Exit via the System screen.\n\n");
 
-    while (quit == 0) {
-        /* Start one asynchronous read on each channel. */
-        bLen = sizeof(bRaw);
-        p_ioc(bchan, P_FREAD, &bStat, bRaw, &bLen);
-        kLen = sizeof(kRaw);
-        p_ioc(kchan, P_FREAD, &kStat, kRaw, &kLen);
-
-        p_iowait();
-
-        /* Keypress? Cancel the scan read and check for Esc. */
-        if (kStat != E_FILE_PENDING) {
-            cancelPending(bchan, &bStat);
-            if (kStat >= 0 && kRaw[0] == KEY_ESC)
-                quit = 1;
+    for (;;) {
+        n = p_read(bchan, raw, sizeof(raw));   /* blocks until bytes arrive */
+        if (n < 0) {
+            p_printf("read error %d\n", n);
             continue;
         }
-
-        /* Scanner delivered bytes. Cancel the keypress read and assemble. */
-        if (bStat != E_FILE_PENDING) {
-            cancelPending(kchan, &kStat);
-            if (bStat >= 0 && bLen > 0) {
-                if (bcodeAssemble(bRaw, (INT)bLen, line, &lineLen, BCODE_MAXLEN)) {
-                    if (upcIsValid(line))
-                        p_printf("OK   %s\n", line);
-                    else
-                        p_printf("BAD  %s  (not a valid UPC-A)\n", line);
-                }
-            }
+        if (bcodeAssemble(raw, n, line, &lineLen, BCODE_MAXLEN)) {
+            textLen = 0;
+            while (line[textLen] != '\0')
+                textLen++;
+            /* Diagnostic: length + text + validity. */
+            if (upcIsValid(line))
+                p_printf("len=%d [%s] OK\n", textLen, line);
+            else
+                p_printf("len=%d [%s] BAD\n", textLen, line);
         }
     }
-
-    p_printf("\nDone.\n");
-    p_close(kchan);
-    bcodeClose(bchan);
-    return 0;
+    /* not reached in this diagnostic build */
 }