--- a/simtool/writecmd.c	Sun Mar 07 04:11:28 2021 +0000
+++ b/simtool/writecmd.c	Sun Mar 07 04:48:37 2021 +0000
@@ -100,3 +100,30 @@
 	}
 	return update_rec_op(recno, mode, data, curfile_record_len);
 }
+
+cmd_update_rec_fill(argc, argv)
+	char **argv;
+{
+	unsigned recno, mode, fill_byte;
+	u_char data[255];
+
+	if (!strcmp(argv[1], "prev")) {
+		recno = 0;
+		mode = 0x03;
+	} else {
+		recno = strtoul(argv[1], 0, 0);
+		if (recno < 1 || recno > 255) {
+			fprintf(stderr,
+			"error: record number argument is out of range\n");
+			return(-1);
+		}
+		mode = 0x04;
+	}
+	fill_byte = strtoul(argv[2], 0, 0);
+	if (fill_byte > 0xFF) {
+		fprintf(stderr, "error: invalid fill byte argument\n");
+		return(-1);
+	}
+	memset(data, fill_byte, curfile_record_len);
+	return update_rec_op(recno, mode, data, curfile_record_len);
+}