micro-controllers

zk/Expressif_IoT_Development_Framework.md

@@ -43,7 +43,7 @@ In any terminal where you want to compile to the device.
 
 ![](../img/esp-32-shell-confirmation.png)
 
-## Compilation process
+## Compilation/flashing process
 
 To demonstrate compilation, I have copied one of the demo projects provided:
 

zk/Serial_transmission.md

@@ -0,0 +1,32 @@
+---
+tags:
+  - computer-architecture
+  - micro-controllers
+---
+
+A serial port/device transmits data sequentially, one bit at a time over a
+single channel/data line.
+
+This is in contrast to parallel transmission, where there are multiple
+channels/data lines, used simultaneously.
+
+With serial transmission, one bit is sent after another:
+
+![Serial transmission](../img/serial-transmission.jpg)
+
+With parallel transmission, each bit of a byte travels on its own channel in
+parallel:
+
+![Parallel transmission](../img/parallel-transmission.jpg)
+
+Although we say a serial device transmits over a single channel, this is a
+logical distinction. The actual electrical signals will be transmitted
+physically via multiple wires.
+
+## Serial devices on Linux
+
+Most serial devices today connect via [USB](./USB_protocols_and_connectors.md).
+
+On Linux, `/dev/ttyUSB*` is a [device](./Devices.md) file representing the
+physical USB connection to a serial device like, for example, an
+[ESP32](./ESP_32.md) microcontroller.