README.md add warning about rp2 USB issue.

diff --git a/README.md b/README.md
index 96c3fce5d185b4005d4b9f57e94c87cc4da88fd4..e2c10d8152d05f871c54492e3fed5a2ac380da20 100644 (file)
--- a/README.md
+++ b/README.md
@@ -15,6 +15,14 @@ then used in an application to send those codes, emulating the remote control.
 Other use cases involve running the receiver in an application. This enables an
 IR remote to control a device such as a robot.
 
+## Raspberry Pi Pico note
+
+Early firmware has [this issue](https://github.com/micropython/micropython/issues/6866)
+affecting USB communication with some PC's. It particularly affects code which
+issues `print()` only occasionally: the application appears to have failed. The
+missing messages appear when you press a key. Hopefully this will be fixed soon
+(note dated 8th March 2021).
+
 #### [Receiver docs](./RECEIVER.md)
 
 The transmitter driver is compatible with Pyboard (1.x and D series) and ESP32.

diff --git a/TRANSMITTER.md b/TRANSMITTER.md
index 1c30d4f7709ce316a8750ef822433211624c6cd1..2093db7155cc7161f9c56370d55f3203c39b3432 100644 (file)
--- a/TRANSMITTER.md
+++ b/TRANSMITTER.md
@@ -47,6 +47,12 @@ updated to use it. The same circuits as above may be used to connect to pin 23
 available on the ESP32 `RMT` object, so any alternative circuit must illuminate
 the LED if the pin state is high.
 
+## 1.3 RP2 Wiring
+
+There is no `active_high` option so the circuit  must illuminate the LED if the
+pin state is high, as per the above drivers. Test programs use pin 17, but this
+can be reassigned.
+
 # 2. Dependencies and installation
 
 ## 2.1 Dependencies