diff --git a/secop_psi/k2601b.py b/secop_psi/k2601b.py
index 6a984e5..d1ad8bc 100644
--- a/secop_psi/k2601b.py
+++ b/secop_psi/k2601b.py
@@ -23,7 +23,7 @@
 not tested yet"""
 
 from secop.core import Attached, BoolType, EnumType, FloatRange, \
-    HasIodev, Module, Parameter, StringIO, Writable
+    HasIodev, Module, Parameter, StringIO, Writable, Done
 
 
 class K2601bIO(StringIO):
@@ -31,13 +31,16 @@ class K2601bIO(StringIO):
 
 
 SOURCECMDS = {
+    0: 'reset()'
+       ' smua.source.func = smua.OUTPUT_DCAMPS'
+       ' display.smua.measure.func = display.MEASURE_VOLTS'
+       ' smua.source.autorangei = 1'
+       ' smua.source.output = %d print("ok"")',
     1: 'reset()'
-       'smua.source.func = smua.OUTPUT_DCVOLTS '
-       'display.smua.measure.func = display.MEASURE_DCAMP '
-       'smua.source.autorangev = 1',
-    2: 'reset()'
-       'smua.source.func = smua.OUTPUT_DCAMPS '
-       'smua.source.autorangei = 1',
+       ' smua.source.func = smua.OUTPUT_DCVOLTS'
+       ' display.smua.measure.func = display.MEASURE_DCAMPS'
+       ' smua.source.autorangev = 1'
+       ' smua.source.output = %d print("ok"")',
 }
 
 
@@ -45,9 +48,8 @@ class SourceMeter(HasIodev, Module):
 
     resistivity = Parameter('readback resistivity', FloatRange(unit='Ohm'), poll=True)
     power = Parameter('readback power', FloatRange(unit='W'), poll=True)
-    mode = Parameter('measurement mode', EnumType(off=0, current=1, voltage=2),
-                     readonly=False, default=0)
-    active = Parameter('output enable', BoolType(), readonly=False, poll=True)
+    mode = Parameter('measurement mode', EnumType(current_off=0, voltage_off=1, current_on=2, voltage_on=3),
+                     readonly=False, poll=True)
 
     iodevClass = K2601bIO
 
@@ -57,20 +59,12 @@ class SourceMeter(HasIodev, Module):
     def read_power(self):
         return self.sendRecv('print(smua.measure.p())')
 
-    def read_active(self):
-        return self.sendRecv('print(smua.source.output)')
-
-    def write_active(self, value):
-        return self.sendRecv('smua.source.output = %d print(smua.source.output)' % value)
-
-    # for now, mode will not be read from hardware
+    def read_mode(self):
+        return float(self.sendRecv('print(smua.source.func+2*smua.source.output)'))
 
     def write_mode(self, value):
-        if value == 0:
-            self.write_active(0)
-        else:
-            self.sendRecv(SOURCECMDS[value] + ' print(0)')
-        return value
+        assert 'ok' == self.sendRecv(SOURCECMDS[value % 2] % (value >= 2))
+        return self.read_mode()
 
 
 class Current(HasIodev, Writable):
@@ -78,9 +72,12 @@ class Current(HasIodev, Writable):
 
     value = Parameter('measured current', FloatRange(unit='A'), poll=True)
     target = Parameter('set current', FloatRange(unit='A'), poll=True)
-    active = Parameter('current is controlled', BoolType(), default=False)  # polled from Current/Voltage
+    active = Parameter('current is controlled', BoolType(), default=False)  # polled by SourceMeter
     limit = Parameter('current limit', FloatRange(0, 2.0, unit='A'), default=2, poll=True)
 
+    def initModule(self):
+        self._sourcemeter.registerCallbacks(self)
+
     def read_value(self):
         return self.sendRecv('print(smua.measure.i())')
 
@@ -104,16 +101,16 @@ class Current(HasIodev, Writable):
             return value
         return self.sendRecv('smua.source.limiti = %g print(smua.source.limiti)' % value)
 
-    def read_active(self):
-        return self._sourcemeter.mode == 1 and self._sourcemeter.read_active()
-
     def write_active(self, value):
-        if self._sourcemeter.mode != 1:
-            if value:
-                self._sourcemeter.write_mode(1)  # switch to current
-            else:
-                return 0
-        return self._sourcemeter.write_active(value)
+        if value:
+            self._sourcemeter.write_mode('current_on')
+        elif self._sourcemeter.mode == 'current_on':
+            self._sourcemeter.write_mode('current_off')
+        return self.active
+
+    def update_mode(self, mode):
+        # will be called whenever the attached sourcemeters mode changes
+        self.active = mode == 'current_on'
 
 
 class Voltage(HasIodev, Writable):
@@ -121,9 +118,12 @@ class Voltage(HasIodev, Writable):
 
     value = Parameter('measured voltage', FloatRange(unit='V'), poll=True)
     target = Parameter('set voltage', FloatRange(unit='V'), poll=True)
-    active = Parameter('voltage is controlled', BoolType(), poll=True)
+    active = Parameter('voltage is controlled', BoolType(), default=False)  # polled by SourceMeter
     limit = Parameter('current limit', FloatRange(0, 2.0, unit='V'), default=2, poll=True)
 
+    def initModule(self):
+        self._sourcemeter.registerCallbacks(self)
+
     def read_value(self):
         return self.sendRecv('print(smua.measure.v())')
 
@@ -147,13 +147,13 @@ class Voltage(HasIodev, Writable):
             return value
         return self.sendRecv('smua.source.limitv = %g print(smua.source.limitv)' % value)
 
-    def read_active(self):
-        return self._sourcemeter.mode == 2 and self._sourcemeter.read_active()
-
     def write_active(self, value):
-        if self._sourcemeter.mode != 2:
-            if value:
-                self._sourcemeter.write_mode(2)  # switch to voltage
-            else:
-                return 0
-        return self._sourcemeter.write_active(value)
+        if value:
+            self._sourcemeter.write_mode('voltage_on')
+        elif self._sourcemeter.mode == 'voltage_on':
+            self._sourcemeter.write_mode('voltage_off')
+        return self.active
+
+    def update_mode(self, mode):
+        # will be called whenever the attached sourcemeters mode changes
+        self.active = mode == 'voltage_on'