Merge pull request #472 from TG9541/TG9541-patch-1

Update README.md

STM8S103F3/README.md

@@ -12,7 +12,7 @@ Note that using this configuration for the [STM8S001J3](https://www.st.com/resou
 
 ## STM8 eForth Programming
 
-Most of the STM8S (RM0016) peripheral registers addresses are the same across "Low density" and "Medium" or "High density" devices and device independent code can be written by using `\res MCU: STM8S`.
+Most of the STM8S (RM0016) peripheral registers addresses are the same across "Low density" and "Medium" or "High density" devices and device independent code can be written by using [`\res MCU: STM8S`](https://github.com/TG9541/stm8ef/blob/master/mcu/STM8S.efr).
 
 Using e4thcom as a terminal program is recommended. With the help of e4thcom (or codeload.py) `mcu/STM8S.efr` can be used to load peripheral register address constants:
 
@@ -21,23 +21,43 @@ Using e4thcom as a terminal program is recommended. With the help of e4thcom (or
 \res export SPI_CR1 SPI_CR2 SPI_DR SPI_SR
 ```
 
-Register addresses of TIM2 and TIM4 are different in STM8S "Low Density" devices. Address constants for these peripherals should then be imported with `\res MCU: STM8S103`.
+Register addresses of TIM2 and TIM4 are different in STM8S "Low Density" devices. Address constants for these peripherals should then be imported with [`\res MCU: STM8S103`](https://github.com/TG9541/stm8ef/blob/master/mcu/STM8S103.efr).
 
-UART constants are again a special case: writing device independent code works best if a sub-set of registers with a `UART_` prefix is used. This can be achieved by using `\res MCU: STM8S103`. The "device independent" `\res MCU: STM8S` can also be used by reassigning constants (e.g. `UART1_DR CONSTANT UART_DR`). More on this in [Some STM8S peripherals are equal, some are the same](https://hackaday.io/project/16097-eforth-for-cheap-stm8s-gadgets/log/178072-some-stm8s-peripherals-are-equal-some-are-the-same) on HaD.
+UART constants are again a special case: writing device independent code works best if a sub-set of registers with a `UART_` prefix is used. This can be achieved by using `\res MCU: STM8S103`. The "device independent" `\res MCU: STM8S` can also be used by reassigning constants (e.g. `UART1_DR CONSTANT UART_DR`). More on this in "[Some STM8S peripherals are equal, some are the same](https://hackaday.io/project/16097-eforth-for-cheap-stm8s-gadgets/log/178072-some-stm8s-peripherals-are-equal-some-are-the-same)" on HaD.
 
 ## USART Console Settings
 
 STM8S "Low density" devices have just one UART, and only STM8S903 devices can remap the UART from the ordinary `PD5/UART_TX` to `PA3/UART_TX` and `PD6/UART_RX` to `PF4/UART_RX` (the STM8S001J3 technically is a STM8S903 chip but it lacks access to `PF4`).
 
 The STM8S103F3 pin description can also be used for the slightly upgraded STM8S903F3 and for STM8S003F3 "Value Line" devices. There are automotive [STM8AF "Low density" devices](https://github.com/TG9541/stm8ef/wiki/STM8-Low-Density-Devices) with mathing or different pin assignments):
+
 ![STM8S103F3](https://user-images.githubusercontent.com/5466977/96366390-b6abe180-1147-11eb-9333-cf47f83759ba.png)
 
 The STM8S903K3 pin functions are a superset of STM8S103K3 (e.g. optional UART pin remapping):
 ![STM8S903K3](https://user-images.githubusercontent.com/5466977/96366224-7730c580-1146-11eb-90da-1230533a9505.png)
 
 Buffered high speed console communication can be added by following the instructions in [`INTRX`](https://github.com/TG9541/stm8ef/blob/master/lib/INTRX) (refer to the `\\ Example` part of the library word).
 
-The STM8S "Low density" UART (`UART1`) can be configured as `HAS_HALFDUPLEX`: by setting `HAS_HALFDUPLEX = 1` in `globconf.inc` the selected USART_TX switches betweens TX and RX:
+### 3-wire serial interface
+
+The default console configuration uses a standard 3-wire serial interface:
+
+```
+               .
+STM8S device   .
+               .
+USRT_TX - ----->>----------o serial TxD "TTL"
+               .             (e.g. "CH340" USB serial converter)
+USRT_RX - ----->>----------o serial RxD "TTL
+               .
+GND ----------->>----------o serial GND
+               .
+```
+Note that console communiaction is actually half-duplex (i.e., the device either processes a command while sending characters on the serial interface, or it listens for the next command).  
+
+### 2-wire serial interface
+
+The STM8S "Low density" UART (`UART1`) supports a 2-wire mode which can be configured by by setting `HAS_HALFDUPLEX = 1` in `globconf.inc` the selected USART_TX switches betweens TX and RX:
 
 ```
                .
@@ -51,9 +71,8 @@ USRT_TX - ----->>-----*----o serial RxD "TTL
                .
 GND ----------->>----------o serial GND
                .
-               .
 ```
 
-This feature can free up one more GPIO for other uses, or it can be used for creating a simple bus.
+This feature frees up a GPIO for other uses, or it can be used for creating a simple bus.
 
 It's also possible to use a simulated serial interface (also in addition to the UART) - please refer to the [SWIMCOM](https://github.com/TG9541/stm8ef/tree/master/SWIMCOM) or the [DOUBLECOM](https://github.com/TG9541/stm8ef/tree/master/DOUBLECOM) configurations.