Changed Tturnaround time in MS/TP modules to be a minimum of 2ms, or use a dummy transmit of 4 bytes while the transceiver is disabled. 1ms delay will always give smaller than 1ms of delay due to silence timer tick.

bacnet-stack/ports/atmega8/rs485.c

@@ -161,15 +161,24 @@ bool RS485_Set_Baud_Rate(
 void RS485_Turnaround_Delay(
     void)
 {
-    uint16_t turnaround_time;
+    uint8_t nbytes = 4;
 
-    /* delay after reception before trasmitting - per MS/TP spec */
-    /* wait a minimum  40 bit times since reception */
-    /* at least 1 ms for errors: rounding, clock tick */
-    turnaround_time = 1 + ((Tturnaround * 1000UL) / RS485_Baud);
-    while (!timer_silence_elapsed(turnaround_time)) {
-        /* do nothing - wait for timer to increment */
-    };
+    RS485_Transmitter_Enable(false);
+    while (nbytes) {
+        while (!BIT_CHECK(UCSR0A, UDRE0)) {
+            /* do nothing - wait until Tx buffer is empty */
+        }
+        /* Send the data byte */
+        UDR0 = 0xff;
+        nbytes--;
+    }
+    /* was the frame sent? */
+    while (!BIT_CHECK(UCSR0A, TXC0)) {
+        /* do nothing - wait until the entire frame in the
+           Transmit Shift Register has been shifted out */
+    }
+    /* Clear the Transmit Complete flag by writing a one to it. */
+    BIT_SET(UCSR0A, TXC0);
 }
 
 /****************************************************************************