diff --git a/doc/SixtyPical.md b/doc/SixtyPical.md
index e0e6624..0cdff8c 100644
--- a/doc/SixtyPical.md
+++ b/doc/SixtyPical.md
@@ -103,6 +103,15 @@ some memory locations causes those memory locations to be uninitialized after
 that routine is called.  At the end of a routine, all memory locations listed
 as outputs must be initialised.
 
+A routine can also be declared as "external", in which case its body need
+not be defined but an absolute address must be given for where the routine
+is located in memory.
+
+    routine chrout
+      inputs a
+      trashes a
+      @ 65490
+
 Instructions
 ------------
 
@@ -291,12 +300,13 @@ Grammar
     Defn    ::= "byte" NewIdent.
     Routine ::= "routine" NewIdent
                 ["inputs" LocExprs] ["outputs" LocExprs] ["trashes" LocExprs]
-                Block.
+                (Block | "@" WordConst).
     LocExprs::= LocExpr {"," LocExpr}.
-    LocExpr ::= Register | Flag | Const | DefnIdent.
+    LocExpr ::= Register | Flag | LitByte | DefnIdent.
     Register::= "a" | "x" | "y".
     Flag    ::= "c" | "z" | "n" | "v".
-    Const   ::= "0" ... "255".
+    LitByte ::= "0" ... "255".
+    LitWord ::= "0" ... "65535".
     Block   ::= "{" {Instr} "}".
     Instr   ::= "ld" LocExpr "," LocExpr
               | "st" LocExpr "," LocExpr
diff --git a/src/sixtypical/parser.py b/src/sixtypical/parser.py
index ac59ac0..8f02e2d 100644
--- a/src/sixtypical/parser.py
+++ b/src/sixtypical/parser.py
@@ -30,7 +30,7 @@ class Scanner(object):
             self.token = None
             self.type = 'EOF'
             return
-        if self.scan_pattern(r'\,|\/|\{|\}', 'operator'):
+        if self.scan_pattern(r'\,|\@|\{|\}', 'operator'):
             return
         if self.scan_pattern(r'\d+', 'integer literal'):
             return
@@ -119,10 +119,17 @@ class Parser(object):
             outputs = self.locexprs()
         if self.scanner.consume('trashes'):
             trashes = self.locexprs()
-        block = self.block()
+        if self.scanner.consume('@'):
+            self.scanner.check_type('integer literal')
+            block = None
+            addr = int(self.scanner.token)
+            self.scanner.scan()
+        else:
+            block = self.block()
+            addr = None
         return Routine(
             name=name, inputs=inputs, outputs=outputs, trashes=trashes,
-            block=block
+            block=block, addr=addr
         )
 
     def locexprs(self):
diff --git a/test.sh b/test.sh
index 587e14a..00c9e71 100755
--- a/test.sh
+++ b/test.sh
@@ -1,6 +1,7 @@
 #!/bin/sh
 
 falderal --substring-error \
+    tests/SixtyPical\ Syntax.md \
     tests/SixtyPical\ Execution.md \
     tests/SixtyPical\ Analysis.md \
     tests/SixtyPical\ Compilation.md
diff --git a/tests/SixtyPical Compilation.md b/tests/SixtyPical Compilation.md
index 3fbdaf9..ab5ef14 100644
--- a/tests/SixtyPical Compilation.md	
+++ b/tests/SixtyPical Compilation.md	
@@ -29,3 +29,20 @@ Rudimentary program.
     |     add a, 4
     | }
     = 00c018690460
+
+Call extern.
+
+    | routine chrout
+    |   inputs a
+    |   trashes a
+    |   @ 65490
+    | 
+    | routine main
+    |   inputs a
+    |   outputs a
+    |   trashes c, z, n, v
+    | {
+    |     ld a, 65
+    |     call chrout
+    | }
+    = 00c018690460
diff --git a/tests/SixtyPical Syntax.md b/tests/SixtyPical Syntax.md
new file mode 100644
index 0000000..b852528
--- /dev/null
+++ b/tests/SixtyPical Syntax.md	
@@ -0,0 +1,41 @@
+Sixtypical Execution
+====================
+
+This is a test suite, written in [Falderal][] format, for the syntax of
+the Sixtypical language, disgregarding execution, static analysis, etc.
+
+[Falderal]:     http://catseye.tc/node/Falderal
+
+    -> Functionality "Check syntax of Sixtypical program" is implemented by
+    -> shell command "bin/sixtypical %(test-body-file) && echo ok"
+
+    -> Tests for functionality "Check syntax of Sixtypical program"
+
+Rudimentary program.
+
+    | routine main {
+    |     ld a, 0
+    |     add a, 1
+    | }
+    = ok
+
+Syntax error
+
+    | routine foo (
+    |     ld a, 0
+    |     add a, 1
+    | )
+    ? SyntaxError
+
+Extern routines
+
+    | routine chrout
+    |   inputs a
+    |   trashes a
+    |   @ 65490
+    | 
+    | routine chrin
+    |   outputs a
+    |   trashes x
+    |   @ 65487
+    = ok