diff --git a/io-module/at91gpio.h b/io-module/at91gpio.h
index c2f8a77..d6328f1 100644
--- a/io-module/at91gpio.h
+++ b/io-module/at91gpio.h
@@ -179,4 +179,23 @@
 #define	AT91_PIN_PE30	(0x80 + 30)
 #define	AT91_PIN_PE31	(0x80 + 31)
 
+// MTCDT-0.2 I2C I/O Port expanders
+#define PCA9557_0_IO0	(0xa0 + 0)
+#define PCA9557_0_IO1	(0xa0 + 1)
+#define PCA9557_0_IO2	(0xa0 + 2)
+#define PCA9557_0_IO3	(0xa0 + 3)
+#define PCA9557_0_IO4	(0xa0 + 4)
+#define PCA9557_0_IO5	(0xa0 + 5)
+#define PCA9557_0_IO6	(0xa0 + 6)
+#define PCA9557_0_IO7	(0xa0 + 7)
+
+#define PCA9557_1_IO0	(0xa8 + 0)
+#define PCA9557_1_IO1	(0xa8 + 1)
+#define PCA9557_1_IO2	(0xa8 + 2)
+#define PCA9557_1_IO3	(0xa8 + 3)
+#define PCA9557_1_IO4	(0xa8 + 4)
+#define PCA9557_1_IO5	(0xa8 + 5)
+#define PCA9557_1_IO6	(0xa8 + 6)
+#define PCA9557_1_IO7	(0xa8 + 7)
+
 #endif