diff --git a/cocas/assembler/targets/cdm16/target_instructions.py b/cocas/assembler/targets/cdm16/target_instructions.py
index 70c886e5..014cecb6 100644
--- a/cocas/assembler/targets/cdm16/target_instructions.py
+++ b/cocas/assembler/targets/cdm16/target_instructions.py
@@ -335,9 +335,9 @@ def special(line: InstructionNode, temp_storage: dict, _):
         arg = line.arguments[0]
         if len(arg.add_terms) != 0 or len(arg.sub_terms) != 0:
             raise CdmTempException('Const number expected')
-        if arg.const_term < 0:
-            raise CdmTempException('Interrupt number must be not negative')
-        return [InstructionBytesSegment(pack("u3u4s9", 0b100, 0, arg.const_term), line.location)]
+        if not 0 <= arg.const_term < 512:
+            raise CdmTempException('Interrupt number out of range')
+        return [InstructionBytesSegment(pack("u3u4u9", 0b100, 0, arg.const_term), line.location)]
     elif line.mnemonic == 'reset':
         if len(line.arguments) == 0:
             arg = RelocatableExpressionNode(None, [], [], 0)
@@ -348,9 +348,9 @@ def special(line: InstructionNode, temp_storage: dict, _):
             raise CdmTempException(f'Expected 0 or 1 arguments, found {len(line.arguments)}')
         if len(arg.add_terms) != 0 or len(arg.sub_terms) != 0:
             raise CdmTempException('Const number expected')
-        if arg.const_term < 0:
-            raise CdmTempException('Vector number must be not negative')
-        return [InstructionBytesSegment(pack("u3u4s9", 0b100, 1, arg.const_term), line.location)]
+        if not 0 <= arg.const_term < 512:
+            raise CdmTempException('Vector number out of range')
+        return [InstructionBytesSegment(pack("u3u4u9", 0b100, 1, arg.const_term), line.location)]
     elif line.mnemonic == 'addsp':
         assert_count_args(line.arguments, Union[RelocatableExpressionNode, RegisterNode])
         if isinstance(line.arguments[0], RelocatableExpressionNode):