From 14eb4d330810e6a94f5a1229bfcb8448ba979eb2 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Petr=20Krac=C3=ADk?= <petrkr@petrkr.net>
Date: Wed, 12 Jun 2019 11:23:03 +0200
Subject: [PATCH] Simplified BCC Checksum calculation

---
 ZPA_elektromer_UARTtest.ino | 17 +++++------------
 1 file changed, 5 insertions(+), 12 deletions(-)

diff --git a/ZPA_elektromer_UARTtest.ino b/ZPA_elektromer_UARTtest.ino
index f4fc101..3682722 100644
--- a/ZPA_elektromer_UARTtest.ino
+++ b/ZPA_elektromer_UARTtest.ino
@@ -84,8 +84,7 @@ void setup() {
 // XOR this value with the second byte, and so forth up to and including the last byte (include 0x03 ETX !!),
 // and XOR the final value with 0xff.
 
-bool firstBCCbyte = false;
-uint8_t localBCC = 0;
+uint8_t localBCC;
 
 void loop() {
 
@@ -97,8 +96,7 @@ void loop() {
 
     if (r == 0x02) {
       Serial.print("<STX>");
-      firstBCCbyte = true;
-      uint8_t localBCC = 0;
+      localBCC = 0xFF; // Set checksum to 0xFF (first byte is XORed with 0xFF)
       return;
     }
 
@@ -108,8 +106,8 @@ void loop() {
       Serial.print(Serial2.read());
       Serial.println();
       Serial.print("Calculated <BCC>: ");
-      localBCC = localBCC ^ 0x03;
-      localBCC = localBCC ^ 0xFF;
+      localBCC = localBCC ^ r;    // Include last byte (ETX) to checksum
+      localBCC = localBCC ^ 0xFF; // Final value XORed with 0xFF
       Serial.print(localBCC);
       Serial.println();
       Serial.println();
@@ -119,12 +117,7 @@ void loop() {
     }
 
     // Calculate BCC checksum
-    if (firstBCCbyte) {
-      firstBCCbyte = false;
-      localBCC = r ^ 0xFF;
-    } else {
-      localBCC = localBCC ^ r;
-    }
+    localBCC = localBCC ^ r;
     Serial.write(r);
   }