diff --git a/DCCRMT.cpp b/DCCRMT.cpp
index cbd9af6..afada7b 100644
--- a/DCCRMT.cpp
+++ b/DCCRMT.cpp
@@ -1,5 +1,5 @@
 /*
- *  © 2021-2022, Harald Barth.
+ *  © 2021-2024, Harald Barth.
  *  
  *  This file is part of DCC-EX
  *
@@ -25,6 +25,18 @@
 #include "DCCWaveform.h" // for MAX_PACKET_SIZE
 #include "soc/gpio_sig_map.h"
 
+// check for right type of ESP32
+#include "soc/soc_caps.h"
+#ifndef SOC_RMT_MEM_WORDS_PER_CHANNEL
+#error This symobol should be defined
+#endif
+#if SOC_RMT_MEM_WORDS_PER_CHANNEL < 64
+#warning This is not an ESP32-WROOM but some other unsupported variant
+#warning You are outside of the DCC-EX supported hardware
+#endif
+
+static const byte RMT_CHAN_PER_DCC_CHAN = 2;
+
 // Number of bits resulting out of X bytes of DCC payload data
 // Each byte has one bit extra and at the end we have one EOF marker
 #define DATA_LEN(X) ((X)*9+1)
@@ -75,12 +87,30 @@ void IRAM_ATTR interrupt(rmt_channel_t channel, void *t) {
 RMTChannel::RMTChannel(pinpair pins, bool isMain) {
   byte ch;
   byte plen;
+
+  // Below we check if the DCC packet actually fits into the RMT hardware
+  // Currently MAX_PACKET_SIZE = 5 so with checksum there are
+  // MAX_PACKET_SIZE+1 data packets. Each need DATA_LEN (9) bits.
+  // To that we add the preamble length, the fencepost DCC end bit
+  // and the RMT EOF marker.
+  // SOC_RMT_MEM_WORDS_PER_CHANNEL is either 64 (original WROOM) or
+  // 48 (all other ESP32 like the -C3 or -S2
+  // The formula to get the possible MAX_PACKET_SIZE is
+  //
+  // ALLOCATED = RMT_CHAN_PER_DCC_CHAN * SOC_RMT_MEM_WORDS_PER_CHANNEL
+  // MAX_PACKET_SIZE = floor((ALLOCATED - PREAMBLE_LEN - 2)/9 - 1)
+  //
+
   if (isMain) {
     ch = 0;
     plen = PREAMBLE_BITS_MAIN;
+    static_assert (DATA_LEN(MAX_PACKET_SIZE+1) + PREAMBLE_BITS_MAIN + 2 <= RMT_CHAN_PER_DCC_CHAN * SOC_RMT_MEM_WORDS_PER_CHANNEL,
+		  "Number of DCC packet bits greater than ESP32 RMT memory available");
   } else {
-    ch = 2;
+    ch = RMT_CHAN_PER_DCC_CHAN; // number == offset
     plen = PREAMBLE_BITS_PROG;
+    static_assert (DATA_LEN(MAX_PACKET_SIZE+1) + PREAMBLE_BITS_PROG + 2 <= RMT_CHAN_PER_DCC_CHAN * SOC_RMT_MEM_WORDS_PER_CHANNEL,
+		   "Number of DCC packet bits greater than ESP32 RMT memory available");
   }
     
   // preamble
@@ -115,7 +145,7 @@ RMTChannel::RMTChannel(pinpair pins, bool isMain) {
   // data: max packet size today is 5 + checksum
   maxDataLen = DATA_LEN(MAX_PACKET_SIZE+1);  // plus checksum
   data = (rmt_item32_t*)malloc(maxDataLen*sizeof(rmt_item32_t));
-  
+
   rmt_config_t config;
   // Configure the RMT channel for TX
   bzero(&config, sizeof(rmt_config_t));
@@ -123,20 +153,10 @@ RMTChannel::RMTChannel(pinpair pins, bool isMain) {
   config.channel = channel = (rmt_channel_t)ch;
   config.clk_div = RMT_CLOCK_DIVIDER;
   config.gpio_num = (gpio_num_t)pins.pin;
-  config.mem_block_num = 2; // With longest DCC packet 11 inc checksum (future expansion)
-                            // number of bits needed is 22preamble + start +
-                            // 11*9 + extrazero + EOT = 124
-                            // 2 mem block of 64 RMT items should be enough
-
+  config.mem_block_num = RMT_CHAN_PER_DCC_CHAN;
+  // use config
   ESP_ERROR_CHECK(rmt_config(&config));
   addPin(pins.invpin, true);
-  /*
-  // test: config another gpio pin
-  gpio_num_t gpioNum = (gpio_num_t)(pin-1);
-  PIN_FUNC_SELECT(GPIO_PIN_MUX_REG[gpioNum], PIN_FUNC_GPIO);
-  gpio_set_direction(gpioNum, GPIO_MODE_OUTPUT);
-  gpio_matrix_out(gpioNum, RMT_SIG_OUT0_IDX, 0, 0);
-  */
   
   // NOTE: ESP_INTR_FLAG_IRAM is *NOT* included in this bitmask
   ESP_ERROR_CHECK(rmt_driver_install(config.channel, 0, ESP_INTR_FLAG_LOWMED|ESP_INTR_FLAG_SHARED));
diff --git a/DCCWaveform.h b/DCCWaveform.h
index 2202b53..1392288 100644
--- a/DCCWaveform.h
+++ b/DCCWaveform.h
@@ -2,7 +2,7 @@
  *  © 2021 M Steve Todd
  *  © 2021 Mike S
  *  © 2021 Fred Decker
- *  © 2020-2021 Harald Barth
+ *  © 2020-2024 Harald Barth
  *  © 2020-2021 Chris Harlow
  *  All rights reserved.
  *  
@@ -33,9 +33,9 @@
 
 
 // Number of preamble bits.
-const int   PREAMBLE_BITS_MAIN = 16;
-const int   PREAMBLE_BITS_PROG = 22;
-const byte   MAX_PACKET_SIZE = 5;  // NMRA standard extended packets, payload size WITHOUT checksum.
+const byte PREAMBLE_BITS_MAIN = 16;
+const byte PREAMBLE_BITS_PROG = 22;
+const byte MAX_PACKET_SIZE = 5;     // NMRA standard extended packets, payload size WITHOUT checksum.
 
 
 // The WAVE_STATE enum is deliberately numbered because a change of order would be catastrophic
diff --git a/EthernetInterface.cpp b/EthernetInterface.cpp
index 993d5d0..914dd8c 100644
--- a/EthernetInterface.cpp
+++ b/EthernetInterface.cpp
@@ -85,9 +85,9 @@ EthernetInterface::EthernetInterface()
     DCCTimer::getSimulatedMacAddress(mac);
     DIAG(F("Ethernet got MAC address"));
   #ifdef IP_ADDRESS
-    if (Ethernet.begin(IP_ADDRESS) == 0)
-  #else
     if (Ethernet.begin(mac, IP_ADDRESS) == 0)
+  #else
+    if (Ethernet.begin(mac) == 0)
   #endif
     {
         DIAG(F("Ethernet.begin FAILED"));
diff --git a/GITHUB_SHA.h b/GITHUB_SHA.h
index 4ece558..1cc285a 100644
--- a/GITHUB_SHA.h
+++ b/GITHUB_SHA.h
@@ -1 +1 @@
-#define GITHUB_SHA "devel-202401030135Z"
+#define GITHUB_SHA "devel-202401081219Z"
diff --git a/version.h b/version.h
index b5eabcf..8239649 100644
--- a/version.h
+++ b/version.h
@@ -3,7 +3,9 @@
 
 #include "StringFormatter.h"
 
-#define VERSION "5.2.18ethCdf"
+#define VERSION "5.2.20ethCdf"
+// 5.2.20 - Check return of Ethernet.begin()
+// 5.2.19 - ESP32: Determine if the RMT hardware can handle DCC
 // 5.2.18 - Display network IP fix
 // 5.2.17 - ESP32 simplify network logic
 // 5.2.16 - Bugfix to allow for devices using the EX-IOExpander protocol to have no analogue or no digital pins