diff --git a/firmware/libboard/octsimtest/include/board.h b/firmware/libboard/octsimtest/include/board.h
index 6006796..361c180 100644
--- a/firmware/libboard/octsimtest/include/board.h
+++ b/firmware/libboard/octsimtest/include/board.h
@@ -62,8 +62,10 @@
 #define PIN_PHONE_IO           {PIO_PA22A_TXD1, PIOA, ID_PIOA, PIO_PERIPH_A, PIO_DEFAULT}
 /* Phone CLK clock input (CLK_PHONE in schematic) */
 #define PIN_PHONE_CLK          {PIO_PA23A_SCK1, PIOA, ID_PIOA, PIO_PERIPH_A, PIO_DEFAULT}
+/* Pin used to switch level shifter in I/O line between rx (0) and tx (1) */
+#define PIN_USIM1_IO_DIR	{PIO_PA16, PIOA, ID_PIOA, PIO_PERIPH_A, PIO_OUTPUT_0}
 /* Pin used for phone USIM slot 1 communication */
-#define PINS_USIM1              PIN_PHONE_IO, PIN_PHONE_CLK, PIN_PHONE_CLK_INPUT, PIN_USIM1_VCC, PIN_PHONE_IO_INPUT, PIN_USIM1_nRST
+#define PINS_USIM1              PIN_PHONE_IO, PIN_PHONE_CLK, PIN_PHONE_CLK_INPUT, PIN_USIM1_VCC, PIN_PHONE_IO_INPUT, PIN_USIM1_nRST, PIN_USIM1_IO_DIR
 /* Phone I/O data signal input/output (unused USART RX input; connected to I/O_PHONE in schematic) */
 #define PIN_PHONE_IO_INPUT     {PIO_PA21A_RXD1, PIOA, ID_PIOA, PIO_PERIPH_A, PIO_DEFAULT}
 /* Pin used as clock input (to measure the ETU duration; connected to CLK_PHONE in schematic) */
diff --git a/firmware/libcommon/source/mode_cardemu.c b/firmware/libcommon/source/mode_cardemu.c
index 127556c..604c66a 100644
--- a/firmware/libcommon/source/mode_cardemu.c
+++ b/firmware/libcommon/source/mode_cardemu.c
@@ -42,6 +42,10 @@
 static const Pin pins_usim1[]	= {PINS_USIM1};
 static const Pin pin_usim1_rst	= PIN_USIM1_nRST;
 static const Pin pin_usim1_vcc	= PIN_USIM1_VCC;
+#ifdef PIN_USIM1_IO_DIR
+static const Pin pin_io_dir 	= PIN_USIM1_IO_DIR;
+#endif
+
 
 #ifdef CARDEMU_SECOND_UART
 static const Pin pins_usim2[]	= {PINS_USIM2};
@@ -142,12 +146,27 @@
 	wait_tx_idle(usart);
 }
 
+static void card_emu_uart_set_direction(uint8_t uart_chan, bool tx)
+{
+	/* only on some boards (octsimtest) we hae an external level
+	 * shifter that requires us to switch the direction between RX and TX */
+#ifdef PIN_USIM1_IO_DIR
+	if (uart_chan == 0) {
+		if (tx)
+			PIO_Set(&pin_io_dir);
+		else
+			PIO_Clear(&pin_io_dir);
+	}
+#endif
+}
+
 /* call-back from card_emu.c to enable/disable transmit and/or receive */
 void card_emu_uart_enable(uint8_t uart_chan, uint8_t rxtx)
 {
 	Usart *usart = get_usart_by_chan(uart_chan);
 	switch (rxtx) {
 	case ENABLE_TX:
+		card_emu_uart_set_direction(uart_chan, true);
 		USART_DisableIt(usart, ~(US_IER_TXRDY | US_IER_TIMEOUT));
 		/* as irritating as it is, we actually want to keep the
 		 * receiver enabled during transmit */
@@ -173,6 +192,7 @@
 		 * transmitter enabled during receive */
 		USART_SetTransmitterEnabled(usart, 1);
 		wait_tx_idle(usart);
+		card_emu_uart_set_direction(uart_chan, false);;
 		usart->US_CR = US_CR_RSTSTA | US_CR_RSTIT | US_CR_RSTNACK;
 		USART_EnableIt(usart, US_IER_RXRDY);
 		USART_SetReceiverEnabled(usart, 1);