diff --git a/README.md b/README.md
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--- a/README.md
+++ b/README.md
@@ -1,27 +1,55 @@
-# build for USB CDC
+# nRF5340 Bluetooth Controller with Support for LE ISO Timesync
+
+This fork of the Zephyr HCI UART example adds a custom HCI Command to allow for timesync between the Bluetooth Host and the Bluetooth Controller. When the HCI LE Read ISO Clock command is received, the Controller toggles a GPIO and returns its current Bluetooth LE ISO Clock in the Command Complete Event.
+
+It has been tested on the nRF5340 Audio DK, but it should work with any nRF5340 dev kit.
+
+## HCI LE Read ISO Clock Command
+- OGF: 0x3f, OCF: 0x200
+- Parameters: Flags (1 Octet) unused
+- Response: HCI Command Complete Event with status and 4 bytes timestamp in microseconds
+
+
+## nRF5340 Development Kit
+
+### HCI over USB CDC
+
 ```sh
 west build -b nrf5340dk_nrf5340_cpuapp -- -DEXTRA_DTC_OVERLAY_FILE=usb.overlay -DOVERLAY_CONFIG=overlay-usb.conf
 ```
+_HCI over UART and timesync not tested._
+
+
+## nRF5340 Audio DK
+
+### HCI over UART 0 connected to Virtual UART in J-Link Probe
 
-# build for build in serial adapter of the nrf5340_audio_dk a.k. uart0
 ```sh
 west build -b nrf5340_audio_dk_nrf5340_cpuapp
 ```
 
-# build for uart1 a.k. arduino_serial
+### HCI over UART 1 connected to Virtual UART in J-Link Probe as well as Arduino Headers
+
+Release build:
 ```sh
 west build -b nrf5340_audio_dk_nrf5340_cpuapp -- -DEXTRA_DTC_OVERLAY_FILE=uart1.overlay
 ```
 
-# build for debug and uart1
+Debug build:
 ```sh
 west build -b nrf5340_audio_dk_nrf5340_cpuapp -- -DEXTRA_DTC_OVERLAY_FILE=uart1.overlay -DOVERLAY_CONFIG=debug.conf
 ```
-# pinout for nrf5340_audio_dk for uart1
 
-| PIN | Arduino |  nrf  |
-|:---:|:-------:|:-----:|
-|  TX |    D0   | P1.09 |
-|  RX |    D1   | P1.08 |
-| RTS |    D7   | P1.11 |
-| CTS |    D8   | P1.10 |
+To use UART 1 via Arduino headers, the virtual UART of the J-Link probe needs to be disabled, e.g. with the JLink Configuration Tool.
+
+### UART 1 + Time Sync Pinout
+
+Signal direction as seen from the nRF5340.
+
+| PIN      | Arduino |  nrf  | Direction |
+|----------|---------|-------|-----------|
+|  TX      |    D0   | P1.09 |    out    |
+|  RX      |    D1   | P1.08 |    in     |
+| RTS      |    D7   | P1.11 |    out    |
+| CTS      |    D8   | P1.10 |    in     |
+| Timesync |    D10  | P1.01 |    out    |