the separator can also be the control character <GS>

Author: nicolaasuni

src/Type/Square/Datamatrix.php

@@ -246,12 +246,18 @@ protected function getHighLevelEncoding(string $data): array
         }
 
         while ($pos < $data_length) {
-            // Determine if current char is FNC1 (don't encode it, just pass it through)
-            if ($this->gsonemode && ($data[$pos] == \chr(232))) {
-                $cdw[] = 232;
-                ++$pos;
-                ++$cdw_num;
-                continue;
+            if ($this->gsonemode) {
+                // check for control characters
+                $cco = \ord($data[$pos]);
+                if (
+                    $cco == 232   // FNC1 (ASCII 232 - HEX \xE8)
+                    || $cco == 29 // <GS> (ASCII  29 - HEX \x1D)
+                ) {
+                    $cdw[] = $cco; // don't encode, just pass it through.
+                    ++$pos;
+                    ++$cdw_num;
+                    continue;
+                }
             }
 
             switch ($enc) {

test/Square/DatamatrixTest.php

@@ -423,8 +423,16 @@ public static function getGridDataProvider(): array
             ],
             [
                 'DATAMATRIX,S,GS1,C40',
+                // \xE8 is the control character FNC1 (ASCII 232)
                 "\xE8" . '01095011010209171719050810ABCD1234' . "\xE8" . '2110',
                 'ba117111dfa40a40e1bb968c719d2eef'
+            ],
+            [
+                'DATAMATRIX,S,GS1',
+                // \xE8 is the control character FNC1 (ASCII 232)
+                // \x1D is the control character <GS> (ASCII 29)
+                "\xE8" . '01095011010209171719050810ABCD1234' . "\x1D" . '2110',
+                'cc096c94e0e2d88e8c50e3fdccef60ce'
             ]
         ];
     }