Fix bug in gca9a01_8_bit.py.

DRIVERS.md

@@ -823,6 +823,15 @@ Clock rates up to 100MHz are supported according to the chip datasheet section
 7.3.4, but high speeds are sensitive to  electrical issues such as lead lengths,
 PCB layout and grounding. I have run 33MHz without issue.
 
+Two versions are provided:
+* `gc9a01.py` 4-bit driver, frame buffer requires 28,800 bytes of RAM.
+* `gc9a01_8_bit.py` 8-bit driver, requires 57,600 bytes.
+
+For use with the three GUI options the 4-bit version is normally preferred. The
+8-bit version allows more colors to be displayed on any given screen. It also
+offers a mode in which 8-bit greyscale full-screen bitmap images can be
+displayed. Both have identical constructor args.
+
 #### GC9A01 Constructor args:
 
  * `spi` An initialised SPI bus instance.
@@ -836,6 +845,19 @@ PCB layout and grounding. I have run 33MHz without issue.
  * `mirror=False` If `True` a mirror-image is displayed
  * `init_spi=False` For shared SPI bus applications. See note below.
 
+ #### Method (8-bit version only)
+
+ * `greyscale(gs=None)` By default the frame buffer contents are interpreted as
+ `rrrgggbb` color values. If `True` is passed, the contents will be treated as
+ 8-bit greyscale values. This mode will persist until the method is called with
+ `False`. Returns the current greyscale state. It is possible to superimpose
+ widgets on an image, but the mapping of colors onto the greyscale may yield
+ unexpected grey values. `WHITE` and `BLACK` work well. In
+ [micro-gui](https://github.com/peterhinch/micropython-micro-gui) and
+ [micropython-touch](https://github.com/peterhinch/micropython-touch) the
+ `after_open` method should be used to render the image to the framebuf and to
+ overlay any widgets.
+
 #### Shared SPI bus
 
 This optional arg enables flexible options in configuring the SPI bus. The

drivers/gc9a01/gc9a01.py

@@ -89,10 +89,9 @@ class GC9A01(framebuf.FrameBuffer):
         # Default page address start == 0 end == 0xEF (239)
         self._wcd(b"\x2b", int.to_bytes(height - 1, 4, "big"))  # SET_PAGE ht
         # **** Start of opaque chip setup ****
-        self._wcmd(b"\xEF")  # Inter register enable 2
-        self._wcd(b"\xEB", b"\x14")  # ?
         self._wcmd(b"\xFE")  # Inter register enable 1
-        self._wcmd(b"\xEF")  # Inter register enable 2
+        self._wcmd(b"\xEF")  # Inter register enable 2. Sequence is necessary
+        # to enable access to other registers.
         self._wcd(b"\xEB", b"\x14")  # ?
         self._wcd(b"\x84", b"\x40")  # ?
         self._wcd(b"\x85", b"\xFF")  # ?
@@ -134,9 +133,9 @@ class GC9A01(framebuf.FrameBuffer):
         self._wcd(b"\x67", b"\x00\x3C\x00\x00\x00\x01\x54\x10\x32\x98")  # Undoc but needed
         self._wcd(b"\x74", b"\x10\x85\x80\x00\x00\x4E\x00")  # ?
         self._wcd(b"\x98", b"\x3e\x07")  # ?
-        self._wcmd(b"\x35")  # Tearing effect line on
-        self._wcmd(b"\x21")  # Display inversion on ???
-        self._wcmd(b"\x11")
+        # self._wcmd(b"\x35")  # Tearing effect line on. This pin is unused.
+        self._wcmd(b"\x21")  # Display inversion on
+        self._wcmd(b"\x11")  # Sleep out
         sleep_ms(120)
         # *************************