For what it's worth

After wasting many hours trying to set the Trickle Charge parameters on my otherwise-obedient DS1302 chips, I eventually realised that I had counterfeit chips.


I've knocked up an Arduino sketch that will try to set the Trickle Charge byte, reporting back on success or failure - users of other hardware can still get the gist:

//written for Uno R3 or Mega
//Tests whether a DS1302 will process a change of the byte controlling Trickle Charge settings (if not, may be a fake)
//John Geddes, February 2016


#include
#include //http://playground.arduino.cc/uploads/Main/DS1302RTC.zip

const int PIN_1302_CE   = A0;   //5;  // Chip Enable
const int PIN_1302_IO   = A1;   //6;  // Input/Output
const int PIN_1302_SCLK = A2;   //7;  // Serial Clock


#define OPTION_TRICKLE_CHARGE_BYTE 0
#define OPTION_YEAR_BYTE 1
byte testResult=0;//score 1 for rtc byte ok, 2 for yeat byte ok. value of 3 means all ok
DS1302RTC my1032rtc(PIN_1302_CE, PIN_1302_IO, PIN_1302_SCLK);

void printPaddedBin(unsigned long thisValue, byte outputLength=8, boolean endLine=false){
  String thisString;
  String netString=String(thisValue,BIN);//no leading zeroes
  byte padCharsRequired=outputLength-netString.length();
  for (byte padCount=0; padCount<(padCharsRequired);padCount++){
    thisString.concat("0");
  }
  Serial.print(thisString);
  Serial.print(netString);
  if (endLine){
    Serial.println();
  }
}

byte toggleByteAndReportOutcome(byte whichByte){
  //returns 1 if ok, otherwise 0
  byte addressWriteByte; //read byte has address one higher
  byte retValIfOK=0;
  String descString;
  byte maxValueBeforeReturningTo1;
  byte valueA;
  byte valueB;
  switch (whichByte){
    case OPTION_TRICKLE_CHARGE_BYTE:
      descString="TRICKLE-CHARGE";
      addressWriteByte=0x90;
      retValIfOK=1;
      valueA=165;
      valueB=166;
      break;
    case OPTION_YEAR_BYTE:
      descString="YEAR";
      addressWriteByte=0x8c;
      retValIfOK=2;
      valueA=B10100001;
      valueB=B10100111;
      break;    
  }
  byte startingByteValue=my1032rtc.readRTC((addressWriteByte+1));
  byte targetByteValue=startingByteValue+1;

  if (startingByteValue==valueA){
    targetByteValue=valueB;
  } else {
    targetByteValue=valueA;
  }

  Serial.print("Attempt to update ");
  Serial.print(descString);
  Serial.print(" byte which currently holds value of ");
  Serial.print(startingByteValue);
  Serial.print(", ie ");
  printPaddedBin(startingByteValue, 8, false);
  Serial.print(" to new value of ");
  Serial.print(targetByteValue);
  Serial.print(", ie ");
  printPaddedBin(targetByteValue, 8, true);

  my1032rtc.writeRTC(addressWriteByte,targetByteValue);
  byte revisedByteValue=my1032rtc.readRTC((addressWriteByte+1));
  if (revisedByteValue==targetByteValue){
    Serial.print("SUCCESS - new value is ");
    Serial.print(revisedByteValue);
    Serial.print(", ie ");
    printPaddedBin(revisedByteValue, 8, true);
    return retValIfOK;
  } else if (revisedByteValue==startingByteValue){
    Serial.print("ERROR - updating has failed: value stayed at ");
    Serial.print(revisedByteValue);
    Serial.print(", ie ");
    printPaddedBin(revisedByteValue, 8, true);
    return 0;
  } else {
    Serial.print("ERROR - updating has failed: value changed but wrong -  at ");
    Serial.print(revisedByteValue);
    Serial.print(", ie ");
    printPaddedBin(revisedByteValue, 8, true);
    return 0;
  }
}


void setup() {
  delay (2000);//time to open Serial Monitor
  Serial.begin(9600);
  Serial.println("DS1302 test started");
  //initialise RTC to be writeable but clock STOPPED
  my1032rtc.writeEN(1);
  Serial.println("DS1302 set to write-enabled");
  my1032rtc.haltRTC(1);//in case this helps
  Serial.println("DS1302 halted");
  testResult+=toggleByteAndReportOutcome(OPTION_TRICKLE_CHARGE_BYTE);
  
  Serial.print("testResult=");
  Serial.println(testResult);
  
  testResult+=toggleByteAndReportOutcome(OPTION_YEAR_BYTE);
  
  Serial.print("testResult=");
  Serial.println(testResult);

  Serial.println("\n");
  switch(testResult){
    case 0:
      Serial.println("Failed both tests: could not update trickle-charge byte or year byte. Check connections");
      break;
    case 1:
      Serial.println ("OK on updating trickle-charge byte but failed on year byte - looks like genuine-but-faulty chip");
      break;
    case 2:
      Serial.println ("Failed to update trickle-charge byte but succeeded with change of year byte - this is the result you get with a FAKE DS1302");
      break;
    case 3:
      Serial.println ("OK on both tests - GENUINE DS1302 working properly");
      break;
  }
}

void loop() {}