diff --git a/vweb/src/lib.rs b/vweb/src/lib.rs
index 744e60d..f51e441 100644
--- a/vweb/src/lib.rs
+++ b/vweb/src/lib.rs
@@ -112,6 +112,8 @@ impl WasmCPU {
         self.0.dp().into()
     }
 
+    pub fn halted(&self) -> bool { self.0.halted() }
+
     pub fn set_pc(&mut self, val: u32) {
         self.0.set_pc(Word::from(val))
     }
@@ -127,4 +129,16 @@ impl WasmCPU {
 
         self.set_pc(0x400)
     }
+
+    pub fn reset(&mut self) {
+        self.0.reset()
+    }
+
+    pub fn start(&mut self) {
+        self.0.start()
+    }
+
+    pub fn tick(&mut self) {
+        self.0.tick()
+    }
 }
diff --git a/vweb/src/snippet_emulator.css b/vweb/src/snippet_emulator.css
index 96ba395..8cd43cc 100644
--- a/vweb/src/snippet_emulator.css
+++ b/vweb/src/snippet_emulator.css
@@ -35,7 +35,10 @@ body {
 .snippetEmulator .buttons a {
     margin-right: 0.5em;
     cursor: pointer;
+    user-select: none;
 }
 .snippetEmulator .step, .snippetEmulator .run { color: lightgreen }
 .snippetEmulator .reset { color: lightcoral }
 .snippetEmulator .build, .snippetEmulator .edit { color: dodgerblue }
+.snippetEmulator .highlight { background-color: darkgoldenrod }
+.snippetEmulator .src { overflow: scroll }
\ No newline at end of file
diff --git a/vweb/src/snippet_emulator.jsx b/vweb/src/snippet_emulator.jsx
index b413333..ffacec3 100644
--- a/vweb/src/snippet_emulator.jsx
+++ b/vweb/src/snippet_emulator.jsx
@@ -1,6 +1,6 @@
 import './snippet_emulator.css'
 import React, {useState, useCallback, useEffect} from 'react'
-import { WasmCPU, assemble_snippet, source_map } from '../pkg/vweb.js'
+import {WasmCPU, assemble_snippet, source_map, NovaForth} from '../pkg/vweb.js'
 
 export default function({ children }) {
     if (React.Children.count(children) !== 1) {
@@ -12,7 +12,19 @@ export default function({ children }) {
     const [message, setMessage] = useState('') // A status / error message
     const onChangeSrc = useCallback((e) => setSrc(e.target.value), []) // Callback for the textarea
     const [binary, setBinary] = useState(null) // The assembled binary
-    const [sourceMap, setSourceMap] = useState({}) // A map from byte address to line number
+    const [sourceMap, setSourceMap] = useState(null) // A map from byte address to line number
+    const [cpu, setCpu] = useState(new WasmCPU()) // The actual CPU emulator itself
+    const [activeLine, setActiveLine] = useState(null) // The (0-based) index of the
+
+    const updateActiveLine = useCallback(() => {
+        sourceMap && setActiveLine(sourceMap.get(cpu.pc()))
+    }, [cpu, sourceMap])
+
+    const reset = useCallback(() => {
+        cpu.reset()
+        cpu.start()
+        updateActiveLine()
+    }, [cpu, updateActiveLine])
 
     // A callback to build the binary from source
     const rebuild = useCallback((code) => {
@@ -20,7 +32,7 @@ export default function({ children }) {
             const bin = assemble_snippet(code)
             const sm = source_map(code)
             setBinary(bin)
-            setSourceMap(sm)
+            setSourceMap(sm.Ok || {})
             setMessage(`Assembled ${bin.length} bytes`)
             return true
         } catch(e) {
@@ -28,13 +40,26 @@ export default function({ children }) {
         }
     }, [])
 
+    const step = useCallback(() => {
+        cpu.tick()
+        updateActiveLine()
+    }, [cpu, updateActiveLine])
+
     // On load, clean the source and build the stuff
     useEffect(() => {
         const lines = React.Children.toArray(children)[0].split('\n')
         const cleaned = lines.map(l => l.trim()).join('\n')
         setSrc(cleaned)
         rebuild(cleaned)
-    }, [rebuild, children])
+    }, [children])
+
+    // Load and reset the CPU when the assembled binary changes
+    useEffect(() => {
+        if (binary) {
+            cpu.load(binary)
+            reset()
+        }
+    }, [cpu, binary, reset])
 
     if (editing) {
         return (
@@ -49,12 +74,12 @@ export default function({ children }) {
     } else {
         return (
             <div className='snippetEmulator'>
-                <SourceDisplay src={src}/>
+                <SourceDisplay src={src} activeLine={activeLine}/>
                 <div className='message'>{message}</div>
                 <div className='buttons'>
-                    <a className='step'>[Step]</a>
+                    <a className='step' onClick={step}>[Step]</a>
                     <a className='step'>[Run]</a>
-                    <a className='reset'>[Reset]</a>
+                    <a className='reset' onClick={reset}>[Reset]</a>
                     <a className='edit' onClick={() => { setEditing(true); setMessage('') }}>[Edit]</a>
                 </div>
             </div>
@@ -62,10 +87,11 @@ export default function({ children }) {
     }
 }
 
-function SourceDisplay({ src }) {
+function SourceDisplay({ src, activeLine }) {
     const lines = src.split('\n')
     const lineDivs = lines.map((line, i) => {
-        return (<div key={`line_${i}`}>{line || <>&nbsp;</>}</div>)
+        // Loop indices are from 0, activeLine numbers are from 1
+        return (<div key={`line_${i}`} className={i + 1 === activeLine ? 'highlight' : ''}>{line || <>&nbsp;</>}</div>)
     })
     return (
         <div className='src'>{lineDivs}</div>