diff --git a/drivers/sharp/README.md b/drivers/sharp/README.md
index c183393..d170f29 100644
--- a/drivers/sharp/README.md
+++ b/drivers/sharp/README.md
@@ -7,7 +7,7 @@ These monochrome SPI displays exist in three variants from Adafruit.
 
 I have tested on the first of these. However the
 [Adfruit driver](https://github.com/adafruit/Adafruit_CircuitPython_SharpMemoryDisplay)
-supports all of these and I would expect this one to do so.
+supports all of these and I would expect this one also to do so.
 
 # 1. Display characteristics
 
@@ -24,9 +24,9 @@ in comparison to stop mode and battery powered applications should be easily
 realised.
 
 The 2.7" display has excellent resolution and can display fine lines and small
-fonts. However the display quality is not as good as ePaper. For good contrast
-best results are achieved if the viewing angle and the direction of the light
-source are positioned to achieve reflection.
+fonts. In other respects the display quality is not as good as ePaper. For good
+contrast best results are achieved if the viewing angle and the direction of
+the light source are positioned to achieve reflection.
 
 ## 1.1 The VCOM bit
 
@@ -63,21 +63,68 @@ In my opinion the easiest way to deal with this is usually to use software
 control, ensuring that the driver's `show` method is called at regular
 intervals of at least 1Hz.
 
+## 1.2 Refresh rate
+
+The datasheet specifies a minimum refresh rate of 1Hz.
+
 # 2. Test scripts
 
  1. `sharptest.py` Basic functionality test.
  2. `clocktest.py` Digital and analog clock display.
+ 3. `clock_batt.py` As above but designed for low power operation.
 
 `sharptest` should not be run for long periods as it does not regularly refresh
 the display. It tests `writer.py` and some `framebuffer` graphics primitives.
 `clocktest` tests `nanogui.py`.
 
 To run the tests the fonts in the directory, `writer.py` and `nanogui.py` must
-be copied to the device or frozen as bytecode. Testing was done on a Pyboard D
-SF6W: frozen bytecode was not required. I suspect a Pyboard 1.x would require
-it to prevent memory errors.
+be copied to the device or frozen as bytecode. The `clack_batt.py` demo needs
+`upower.py` from
+[micropython-micropower](https://github.com/peterhinch/micropython-micropower).
 
-# 3. Resources
+Testing was done on a Pyboard D SF6W: frozen bytecode was not required. I
+suspect a Pyboard 1.x would require it to prevent memory errors.
+
+# 3. Device driver constructor
+
+Positional args:
+ 1. `spi` An SPI bus instance. The constructor initialises this to the baudrate
+ and bit order required by the hardware.
+ 2. `pincs` A `Pin` instance. The caller should initialise this as an output
+ with value 0 (unusually the hardware CS line is active high).
+ 3. `height=240` Dimensions in pixels. Defaults are for 2.7" display.
+ 4. `width=400`
+ 5. `vcom=False` Accept the default unless using `pyb.standby`. See 3.2.
+
+# 3.1 Device driver methods
+
+ 1. `show` No args. Transfers the framebuffer contents to the device, updating
+ the display.
+ 2. `update` Toggles the `VCOM` bit without transferring the framebuffer. This
+ is a power saving method for cases where the application calls `show` at a
+ rate of < 1Hz. In such cases `update` should be called at a 1Hz rate.
+
+# 3.2 The vcom arg
+
+It purpose is to support micropower applications which use `pyb.standby`.
+Wakeup from standby is similar to a reboot in that program execution starts
+from scratch. In the case where the board wakes up, writes to the display, and
+returns to standby, the `VCOM` bit would never change. In this case the
+application should store a `bool` in peristent storage, toggling it on each
+restart, and pass that to the constructor.
+
+Persistent storage exists in the RTC registers and backup RAM. See
+[micopython-micropower](https://github.com/peterhinch/micropython-micropower)
+for details of how to acces these resources.
+
+# 4. Application design
+
+In all cases the frame buffer is located on the target hardware. In the case of
+the 2.7 inch display this is 400*240//8 = 12000 bytes in size. This should be
+instantiated as soon as possible in the application to ensure that sufficient
+contiguous RAM is available.
+
+# 5. Resources
 
 [Schematic for 2.7" unit](https://learn.adafruit.com/assets/94077)
 
diff --git a/drivers/sharp/clock_batt.py b/drivers/sharp/clock_batt.py
new file mode 100644
index 0000000..32ae7a9
--- /dev/null
+++ b/drivers/sharp/clock_batt.py
@@ -0,0 +1,87 @@
+# clock_batt.py Battery powered clock demo for Pyboard/Adafruit sharp 2.7" display
+
+# Copyright (c) 2020 Peter Hinch
+# Released under the MIT license. See LICENSE
+
+# HARDWARE
+# This assumes a Pybaord D in WBUS-DIP28 and powered by a LiPo cell
+# WIRING
+# Pyb   SSD
+# Vin   Vin  Pyboard D: Vin on DIP28 is an output when powered by LiPo
+# Gnd   Gnd
+# Y8    DI
+# Y6    CLK
+# Y5    CS
+
+
+# Demo of initialisation procedure designed to minimise risk of memory fail
+# when instantiating the frame buffer. The aim is to do this as early as
+# possible before importing other modules.
+
+import machine
+import gc
+from sharp import SHARP as SSD
+
+# Initialise hardware
+pcs = machine.Pin('Y5', machine.Pin.OUT_PP, value=0)  # Active high
+spi = machine.SPI(2)
+gc.collect()  # Precaution before instantiating framebuf
+ssd = SSD(spi, pcs)
+
+# Now import other modules
+import upower
+from nanogui import Dial, Pointer, refresh, Label
+import pyb
+import cmath
+from writer import Writer
+
+# Fonts for Writer
+import freesans20 as font_small
+import arial35 as font_large
+
+refresh(ssd)  # Initialise display.
+
+def aclock():
+    rtc = pyb.RTC()
+    uv = lambda phi : cmath.rect(1, phi)  # Return a unit vector of phase phi
+    pi = cmath.pi
+    days = ('Mon', 'Tue', 'Wed', 'Thur', 'Fri', 'Sat', 'Sun')
+    months = ('Jan', 'Feb', 'March', 'April', 'May', 'June', 'July',
+              'Aug', 'Sept', 'Oct', 'Nov', 'Dec')
+    # Instantiate Writer
+    Writer.set_textpos(ssd, 0, 0)  # In case previous tests have altered it
+    wri = Writer(ssd, font_small, verbose=False)
+    wri.set_clip(True, True, False)
+    wri_tim = Writer(ssd, font_large, verbose=False)
+    wri_tim.set_clip(True, True, False)
+
+    # Instantiate displayable objects
+    dial = Dial(wri, 2, 2, height = 215, ticks = 12, bdcolor=None, pip=True)
+    lbltim = Label(wri_tim, 50, 230, '00.00.00')
+    lbldat = Label(wri, 100, 230, 100)
+    hrs = Pointer(dial)
+    mins = Pointer(dial)
+    secs = Pointer(dial)
+
+    hstart =  0 + 0.7j  # Pointer lengths and position at top
+    mstart = 0 + 0.92j
+    sstart = 0 + 0.92j 
+    while True:
+        t = rtc.datetime()  # (year, month, day, weekday, hours, minutes, seconds, subseconds)
+        hang = -t[4]*pi/6 - t[5]*pi/360  # Angles of hour and minute hands
+        mang = -t[5] * pi/30
+        sang = -t[6] * pi/30
+        if abs(hang - mang) < pi/360:  # Avoid overlap of hands
+            hang += pi/18
+        hrs.value(hstart * uv(hang))
+        mins.value(mstart * uv(mang))
+        secs.value(sstart * uv(sang))
+        lbltim.value('{:02d}.{:02d}.{:02d}'.format(t[4], t[5], t[6]))
+        lbldat.value('{} {} {} {}'.format(days[t[3] - 1], t[2], months[t[1] - 1], t[0]))
+        refresh(ssd)
+        # Power saving: only refresh every 10s
+        for _ in range(10):
+            upower.lpdelay(1000)
+            ssd.update()  # Toggle VCOM
+
+aclock()
diff --git a/drivers/sharp/clocktest.py b/drivers/sharp/clocktest.py
index f04e0de..7ca8382 100644
--- a/drivers/sharp/clocktest.py
+++ b/drivers/sharp/clocktest.py
@@ -1,36 +1,15 @@
 # clocktest.py Test/demo program for Adafruit sharp 2.7" display
 
 # Copyright (c) 2020 Peter Hinch
+# Released under the MIT license. See LICENSE
 
-# The MIT License (MIT)
-
-# Permission is hereby granted, free of charge, to any person obtaining a copy
-# of this software and associated documentation files (the "Software"), to deal
-# in the Software without restriction, including without limitation the rights
-# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
-# copies of the Software, and to permit persons to whom the Software is
-# furnished to do so, subject to the following conditions:
-#
-# The above copyright notice and this permission notice shall be included in
-# all copies or substantial portions of the Software.
-#
-# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
-# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
-# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
-# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
-# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
-# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
-# THE SOFTWARE.
-
-# WIRING TODO
+# WIRING
 # Pyb   SSD
-# 3v3   Vin
+# Vin   Vin  Pyboard: Vin is an output when powered by USB
 # Gnd   Gnd
-# X1    DC
-# X2    CS
-# X3    Rst
-# X6    CLK
-# X8    DATA
+# Y8    DI
+# Y6    CLK
+# Y5    CS
 
 
 # Demo of initialisation procedure designed to minimise risk of memory fail
@@ -46,17 +25,19 @@ pcs = machine.Pin('Y5', machine.Pin.OUT_PP, value=0)  # Active high
 spi = machine.SPI(2)
 gc.collect()  # Precaution before instantiating framebuf
 ssd = SSD(spi, pcs)
-from nanogui import Dial, Pointer, refresh, Label
-refresh(ssd)  # Initialise and clear display.
 
 # Now import other modules
+from nanogui import Dial, Pointer, refresh, Label
 import cmath
 import utime
 from writer import Writer
 
-# Font for Writer
+# Fonts for Writer
 import freesans20 as font_small
 import arial35 as font_large
+
+refresh(ssd)  # Initialise display.
+
 def aclock():
     uv = lambda phi : cmath.rect(1, phi)  # Return a unit vector of phase phi
     pi = cmath.pi
@@ -83,7 +64,9 @@ def aclock():
     sstart = 0 + 0.92j 
     while True:
         t = utime.localtime()
-        hrs.value(hstart * uv(-t[3]*pi/6 - t[4]*pi/360))
+        # Add 0.5min offset to hour hand. This avoids a confusing display by
+        # ensuring hour and minute hand never exactly overlap
+        hrs.value(hstart * uv(-t[3]*pi/6 - t[4]*pi/360) - pi/720)
         mins.value(mstart * uv(-t[4] * pi/30))
         secs.value(sstart * uv(-t[5] * pi/30))
         lbltim.value('{:02d}.{:02d}.{:02d}'.format(t[3], t[4], t[5]))
diff --git a/drivers/sharp/sharp.py b/drivers/sharp/sharp.py
index 0417830..e80d039 100644
--- a/drivers/sharp/sharp.py
+++ b/drivers/sharp/sharp.py
@@ -24,22 +24,22 @@ _VCOM = const(2)
 
 class SHARP(framebuf.FrameBuffer):
 
-    def __init__(self, spi, pincs):
+    def __init__(self, spi, pincs, height=240, width=400, vcom=False):
         spi.init(baudrate=2_000_000, firstbit=machine.SPI.LSB)  # Data sheet: should support 2MHz
         self._spi = spi
         self._pincs = pincs
-        self.height = 240  # Required by Writer class and nanogui
-        self.width = 400
+        self.height = height  # Required by Writer class and nanogui
+        self.width = width
         self._buffer = bytearray(self.height * self.width // 8)
         self._mvb = memoryview(self._buffer)
         super().__init__(self._buffer, self.width, self.height, framebuf.MONO_HMSB)
         self._cmd = bytearray(1)  # Buffer for command. Holds current VCOM bit
-        self._cmd[0] = _WRITECMD
+        self._cmd[0] = _WRITECMD | _VCOM if vcom else _WRITECMD
         self._lno = bytearray(1)  # Line no.
         self._dummy = bytearray(1)  # Dummy (0)
 
     # .show should be called periodically to avoid frame inversion flag
-    # retaining the same value for long periods
+    # (VCOM) retaining the same value for long periods
     def show(self):
         spi = self._spi
         bpl = self.width // 8  # Bytes per line
@@ -57,3 +57,11 @@ class SHARP(framebuf.FrameBuffer):
         spi.write(self._dummy)
         self._pincs(0)
         self._cmd[0] ^= _VCOM  # Toggle frame inversion flag
+
+    # Toggle the VCOM bit without changing the display. Power saving method.
+    def update(self):
+        self._pincs(1)
+        self._lno[0] = self._cmd[0] & _VCOM
+        self._spi.write(self._lno)
+        self._cmd[0] ^= _VCOM  # Toggle frame inversion flag
+        self._pincs(0)
diff --git a/drivers/sharp/sharptest.py b/drivers/sharp/sharptest.py
index a3adcd7..be9621b 100644
--- a/drivers/sharp/sharptest.py
+++ b/drivers/sharp/sharptest.py
@@ -5,6 +5,13 @@
 # Copyright (c) Peter Hinch 2020
 # Released under the MIT license see LICENSE
 
+# WIRING
+# Pyb   SSD
+# Vin   Vin  Pyboard: Vin is an output when powered by USB
+# Gnd   Gnd
+# Y8    DI
+# Y6    CLK
+# Y5    CS
 
 import machine
 from sharp import SHARP