Add single char wait time after flush to avoid RTU control pin timing…

… issue, see #68 and #72

changelog.md

@@ -15,6 +15,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 <!-- ## [Unreleased] -->
 
 ## Released
+## [2.3.7] - 2023-07-19
+### Fixed
+- Add a single character wait time after flush to avoid timing issues with RTU control pin, see #68 and #72
+
 ## [2.3.6] - 2023-07-19
 ### Added
 - Add contribution guideline, see #67
@@ -303,8 +307,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - PEP8 style issues on all files of [`lib/uModbus`](lib/uModbus)
 
 <!-- Links -->
-[Unreleased]: https://github.com/brainelectronics/micropython-modbus/compare/2.3.6...develop
+[Unreleased]: https://github.com/brainelectronics/micropython-modbus/compare/2.3.7...develop
 
+[2.3.7]: https://github.com/brainelectronics/micropython-modbus/tree/2.3.7
 [2.3.6]: https://github.com/brainelectronics/micropython-modbus/tree/2.3.6
 [2.3.5]: https://github.com/brainelectronics/micropython-modbus/tree/2.3.5
 [2.3.4]: https://github.com/brainelectronics/micropython-modbus/tree/2.3.4

umodbus/serial.py

@@ -274,8 +274,10 @@ def _send(self, modbus_pdu: bytes, slave_addr: int) -> None:
         # 360-400us @ 9600-115200 baud (measured) (ESP32 @ 160/240MHz)
         self._uart.write(modbus_adu)
         send_finish_time = time.ticks_us()
+
         if self._has_uart_flush:
             self._uart.flush()
+            time.sleep_us(self._t1char)
         else:
             sleep_time_us = (
                 self._t1char * len(modbus_adu) -    # total frame time in us