diff --git a/dc11.cpp b/dc11.cpp
index 5caebda..26c5b16 100644
--- a/dc11.cpp
+++ b/dc11.cpp
@@ -137,6 +137,31 @@ void dc11::show_state(console *const cnsl) const
 	}
 }
 
+void dc11::test_serial(const std::string & txt) const
+{
+	for(int i=0; i<dc11_n_lines; i++) {
+		if (i == serial_line) {
+			DOLOG(info, false, "DC11 serial test line %d", i);
+
+#if defined(ESP32)
+			uart_write_bytes(ESP32_UART, txt.c_str(), txt.size());
+#elif IS_POSIX
+			if (write(serial_fd, txt.c_str(), txt.size()) != txt.size())
+				DOLOG(warning, false, "DC11 failed to send test string to line %d", i);
+#endif
+		}
+		else if (pfds[dc11_n_lines + i].fd != INVALID_SOCKET) {
+			DOLOG(info, false, "DC11 socket line %d", i);
+
+			if (write(pfds[dc11_n_lines + i].fd, txt.c_str(), txt.size()) != txt.size())
+				DOLOG(warning, false, "DC11 failed to send test string to line %d", i);
+		}
+		else {
+			DOLOG(info, false, "DC11 line %d not connected", i);
+		}
+	}
+}
+
 void dc11::trigger_interrupt(const int line_nr, const bool is_tx)
 {
 	TRACE("DC11: interrupt for line %d, %s", line_nr, is_tx ? "TX" : "RX");
diff --git a/dc11.h b/dc11.h
index fc23436..1440c2a 100644
--- a/dc11.h
+++ b/dc11.h
@@ -73,6 +73,8 @@ public:
 
 	void show_state(console *const cnsl) const override;
 
+	void test_serial(const std::string & txt) const;
+
 #if defined(ESP32)
 	void set_serial(const int bitrate, const int rx, const int tx);
 	void serial_handler();
diff --git a/debugger.cpp b/debugger.cpp
index 281ec0d..8381f69 100644
--- a/debugger.cpp
+++ b/debugger.cpp
@@ -970,6 +970,11 @@ void debugger(console *const cnsl, bus *const b, std::atomic_uint32_t *const sto
 
 				continue;
 			}
+			else if (parts[0] == "testdc11") {
+				b->getDC11()->test_serial(cmd);
+
+				continue;
+			}
 			else if (cmd == "dp") {
 				cnsl->stop_panel_thread();
 
@@ -1040,6 +1045,7 @@ void debugger(console *const cnsl, bus *const b, std::atomic_uint32_t *const sto
 					"startnet      - start network",
 					"chknet        - check network status",
 #endif
+					"testdc11      - test DC11",
 					"cfgdisk       - configure disk",
 					"log ...       - log a message to the logfile",
 					nullptr