diff --git a/include/gpsread.h b/include/gpsread.h
index 3cd4a931..9fccefb4 100644
--- a/include/gpsread.h
+++ b/include/gpsread.h
@@ -16,5 +16,6 @@ int gps_init(void);
 void gps_read(void);
 void gps_loop(void *pvParameters);
 time_t get_gpstime(void);
+int gps_config();
 
 #endif
\ No newline at end of file
diff --git a/platformio.ini b/platformio.ini
index dc5b8873..e28b6047 100644
--- a/platformio.ini
+++ b/platformio.ini
@@ -15,8 +15,8 @@
 ;env_default = ttgov2
 ;env_default = ttgov21old
 ;env_default = ttgov21new
-env_default = ttgobeam
-;env_default = ttgofox
+;env_default = ttgobeam
+env_default = ttgofox
 ;env_default = lopy
 ;env_default = lopy4
 ;env_default = fipy
@@ -50,6 +50,7 @@ lib_deps_rgbled =
     SmartLeds@>=1.1.5
 lib_deps_gps =
     TinyGPSPlus@>=1.0.2
+;    NeoGPS^4.2.9
 lib_deps_rtc =
     RTC@^2.3.0
 lib_deps_basic =
@@ -222,6 +223,7 @@ build_flags =
 upload_protocol = ${common.upload_protocol}
 extra_scripts = ${common.extra_scripts}
 monitor_speed = ${common.monitor_speed}
+upload_port = COM61
 
 [env:ttgobeam]
 platform = ${common.platform_espressif32}
diff --git a/src/dcf77.cpp b/src/dcf77.cpp
index 0648d854..a4b1c62a 100644
--- a/src/dcf77.cpp
+++ b/src/dcf77.cpp
@@ -20,8 +20,11 @@ static const char TAG[] = "main";
 #define DCF77_FRAME_SIZE (60)
 #define DCF77_PULSE_DURATION (100)
 
+// select internal / external clock
 #if defined RTC_INT && defined RTC_CLK
 #define PPS RTC_CLK
+#elif defined GPS_INT && defined GPS_CLK
+#define PPS GPS_CLK
 #else
 #define PPS DCF77_PULSE_DURATION
 #endif
@@ -127,13 +130,16 @@ void dcf77_loop(void *pvParameters) {
         &wakeTime,      // receives moment of call from isr
         portMAX_DELAY); // wait forever (missing error handling here...)
 
+// select clock scale
 #if (PPS == DCF77_PULSE_DURATION) // we don't need clock rescaling
     DCF_Out(0);
+
 #elif (PPS > DCF77_PULSE_DURATION) // we need upclocking
     for (uint8_t i = 1; i <= PPS / DCF77_PULSE_DURATION; i++) {
       DCF_Out(0);
       vTaskDelayUntil(&wakeTime, pdMS_TO_TICKS(DCF77_PULSE_DURATION));
     }
+
 #elif (PPS < DCF77_PULSE_DURATION) // we need downclocking
     vTaskDelayUntil(&wakeTime, pdMS_TO_TICKS(DCF77_PULSE_DURATION - PPS));
     DCF_Out(0);
diff --git a/src/gpsread.cpp b/src/gpsread.cpp
index a446118e..6e094faf 100644
--- a/src/gpsread.cpp
+++ b/src/gpsread.cpp
@@ -18,6 +18,11 @@ int gps_init(void) {
 
   int ret = 1;
 
+  if (!gps_config()) {
+    ESP_LOGE(TAG, "GPS chip initializiation error");
+    return 0;
+  }
+
 #if defined GPS_SERIAL
   GPS_Serial.begin(GPS_SERIAL);
   ESP_LOGI(TAG, "Using serial GPS");
@@ -41,6 +46,21 @@ int gps_init(void) {
   return ret;
 } // gps_init()
 
+// detect gps chipset type and configure it with device specific settings
+int gps_config() {
+  int rslt = 1; // success
+#if defined GPS_SERIAL
+
+  /* to come */
+
+#elif defined GPS_I2C
+
+  /* to come */
+
+#endif
+  return rslt;
+}
+
 // read GPS data and cast to global struct
 void gps_read() {
   gps_status.latitude = (int32_t)(gps.location.lat() * 1e6);
@@ -73,8 +93,8 @@ time_t get_gpstime(void) {
   if ((gps.time.age() < 1500) && (gps.time.isValid())) {
     t = tmConvert_t(gps.date.year(), gps.date.month(), gps.date.day(),
                     gps.time.hour(), gps.time.minute(), gps.time.second());
-    ESP_LOGD(TAG, "GPS time: %4d/%02d/%02d %02d:%02d:%02d", year(t), month(t), day(t),
-             hour(t), minute(t), second(t));
+    ESP_LOGD(TAG, "GPS time: %4d/%02d/%02d %02d:%02d:%02d", year(t), month(t),
+             day(t), hour(t), minute(t), second(t));
   } else {
     ESP_LOGW(TAG, "GPS has no confident time");
   }
diff --git a/src/hal/ttgobeam.h b/src/hal/ttgobeam.h
index f49eb27e..c32994a8 100644
--- a/src/hal/ttgobeam.h
+++ b/src/hal/ttgobeam.h
@@ -19,8 +19,14 @@
 #define HAS_BUTTON GPIO_NUM_39 // on board button (next to reset)
 #define HAS_BATTERY_PROBE ADC1_GPIO35_CHANNEL // battery probe GPIO pin -> ADC1_CHANNEL_7
 #define BATT_FACTOR 2 // voltage divider 100k/100k on board
+
+// GPS settings
 #define HAS_GPS 1 // use on board GPS
 #define GPS_SERIAL 9600, SERIAL_8N1, GPIO_NUM_12, GPIO_NUM_15 // UBlox NEO 6M or 7M with default configuration
+// to use 
+#define GPS_INT GPIO_NUM_34 // 30ns accurary timepulse, to be external wired on pcb: R34 -> GPIO34
+// 1 pulse per second, synchronized at rising edge, pulse length 100ms, accuracy +/- 3 *e-8 [nanoseconds] = 0,95sec / year
+#define GPS_CLK (1000)
 
 // enable only if device has these sensors, otherwise comment these lines
 // BME680 sensor on I2C bus
@@ -35,7 +41,11 @@
 //#define DISPLAY_FLIP  1 // use if display is rotated
 
 // Settings for DCF77 interface
-#define HAS_DCF77 GPIO_NUM_13
+//#define HAS_DCF77 GPIO_NUM_13
+
+// Settings for IF482 interface
+#define HAS_IF482 9600, SERIAL_7E1, GPIO_NUM_12, GPIO_NUM_14 // IF482 serial port parameters
+
 
 // user defined sensors (if connected)
 //#define HAS_SENSORS 1 // comment out if device has user defined sensors
diff --git a/src/hal/ttgofox.h b/src/hal/ttgofox.h
index f7cd3033..7be3544c 100644
--- a/src/hal/ttgofox.h
+++ b/src/hal/ttgofox.h
@@ -20,12 +20,17 @@
 #define MY_OLED_SCL (22)
 #define MY_OLED_RST U8X8_PIN_NONE
 
-// Pins for on board DS3231 RTC chip
+// Settings for on board DS3231 RTC chip
 #define HAS_RTC MY_OLED_SDA, MY_OLED_SCL // SDA, SCL
-#define RTC_INT GPIO_NUM_34 // interrupt input from rtc
+//#define RTC_INT GPIO_NUM_34 // timepulse with accuracy +/- 2*e-6 [microseconds] = 0,1728sec / day
+//#define RTC_CLK (1000) // frequency of RTC clock signal in ms
 
 // Settings for IF482 interface
-#define HAS_IF482 9600, SERIAL_7E1, GPIO_NUM_12, GPIO_NUM_14 // IF482 serial port parameters
+//#define HAS_IF482 9600, SERIAL_7E1, GPIO_NUM_12, GPIO_NUM_14 // IF482 serial port parameters
+
+// Settings for DCF77 interface
+#define HAS_DCF77 GPIO_NUM_14
+#define DCF77_ACTIVE_LOW 1
 
 // Settings for external GPS chip
 #define HAS_GPS 1 // use on board GPS
diff --git a/src/if482.cpp b/src/if482.cpp
index 71df7a56..600e3fd5 100644
--- a/src/if482.cpp
+++ b/src/if482.cpp
@@ -91,12 +91,16 @@ static const char TAG[] = "main";
 #define IF482_FRAME_SIZE (17)
 #define IF482_PULSE_DURATION (1000)
 
-#ifdef RTC_CLK
+// select internal / external clock
+#if defined RTC_INT && defined RTC_CLK
 #define PPS RTC_CLK
+#elif defined GPS_INT && defined GPS_CLK
+#define PPS GPS_CLK
 #else
 #define PPS IF482_PULSE_DURATION
 #endif
 
+
 HardwareSerial IF482(2); // use UART #2 (note: #1 may be in use for serial GPS)
 
 // initialize and configure IF482 Generator
@@ -175,20 +179,22 @@ void if482_loop(void *pvParameters) {
         &wakeTime,      // receives moment of call from isr
         portMAX_DELAY); // wait forever (missing error handling here...)
 
+// select clock scale
 #if (PPS == IF482_PULSE_DURATION) // we don't need clock rescaling
     // wait until it's time to start transmit telegram for next second
     vTaskDelayUntil(&wakeTime, shotTime); // sets waketime to moment of shot
     IF482.print(IF482_Out(now() + 1));
+
 #elif (PPS > IF482_PULSE_DURATION) // we need upclocking
     for (uint8_t i = 1; i <= PPS / IF482_PULSE_DURATION; i++) {
       vTaskDelayUntil(&wakeTime, shotTime); // sets waketime to moment of shot
       IF482.print(IF482_Out(now() + 1));
     }
+
 #elif (PPS < IF482_PULSE_DURATION) // we need downclocking
     IF482.print(IF482_Out(now() + 1));
     vTaskDelayUntil(&wakeTime,
                     shotTime - PPS); // sets waketime to moment of shot
-
 #endif
   }
 } // if482_loop()
diff --git a/src/rtctime.cpp b/src/rtctime.cpp
index de909866..aee26515 100644
--- a/src/rtctime.cpp
+++ b/src/rtctime.cpp
@@ -102,8 +102,10 @@ float get_rtctemp(void) {
 
 #endif // HAS_RTC
 
-int pps_init(uint32_t clk_freq_ms) {
-// use fixed pulse clock as time base
+// helper function to setup a pulse for time synchronisation
+int pps_init(uint32_t pulse_period_ms) {
+
+// use pulse from on board RTC chip as time base with fixed frequency
 #if defined RTC_INT && defined RTC_CLK
 
   // setup external interupt for active low RTC INT pin
@@ -121,13 +123,16 @@ int pps_init(uint32_t clk_freq_ms) {
   }
   return 1; // success
 
+  #elif defined RTC_INT && defined HAS_GPS
+
 #else
-  // use clock with adjustable frequency
-  if (clk_freq_ms) {
+  // use ESP32 hardware timer as time base with adjustable frequency
+  if (pulse_period_ms) {
     ESP_LOGI(TAG, "Time base ESP32 clock");
-    clockCycle = timerBegin(1, 8000, true); // set 80 MHz prescaler to 1/10000 sec
+    clockCycle =
+        timerBegin(1, 8000, true); // set 80 MHz prescaler to 1/10000 sec
     timerAttachInterrupt(clockCycle, &CLOCKIRQ, true);
-    timerAlarmWrite(clockCycle, 10 * clk_freq_ms, true); //ms
+    timerAlarmWrite(clockCycle, 10 * pulse_period_ms, true); // ms
   } else {
     ESP_LOGE(TAG, "Invalid pulse clock frequency");
     return 0; // failure
@@ -138,7 +143,8 @@ int pps_init(uint32_t clk_freq_ms) {
 
 void pps_start() {
 #ifdef RTC_INT // start external clock
-  attachInterrupt(digitalPinToInterrupt(RTC_INT), CLOCKIRQ, FALLING);
+  //attachInterrupt(digitalPinToInterrupt(RTC_INT), CLOCKIRQ, FALLING);
+  attachInterrupt(digitalPinToInterrupt(RTC_INT), CLOCKIRQ, RISING);
 #else // start internal clock
   timerAlarmEnable(clockCycle);
 #endif