diff --git a/firmware/Makefile.inc b/firmware/Makefile.inc
index 03314b8..3466c3b 100644
--- a/firmware/Makefile.inc
+++ b/firmware/Makefile.inc
@@ -1,4 +1,4 @@
-DEFINES += -DF_CPU=16000000
+#DEFINES += -DF_CPU=16000000
 CFLAGS += -save-temps
 CFLAGS += -std=gnu99 -Wall # implements C99, for <util/atomic.h>
 # this removes dead code and does global linker optimization
diff --git a/firmware/masterchip/Makefile b/firmware/masterchip/Makefile
index 6630a39..f8b9ce8 100644
--- a/firmware/masterchip/Makefile
+++ b/firmware/masterchip/Makefile
@@ -1,6 +1,8 @@
 # masterchip-makefile
 include ../Makefile.inc
 
+DEFINES += -DF_CPU=16000000
+
 COMPILE = avr-gcc $(CFLAGS) $(DEFINES)
 
 OBJECTS = usbdrv/usbdrvasm.o usbdrv/usbdrv.o main.o display.o lcd/lcd.o usb.o softtimer.o spi.o spi_proto.o spi_pointers.o
diff --git a/firmware/slavechip/Makefile b/firmware/slavechip/Makefile
index 0e0fe40..0d9d531 100644
--- a/firmware/slavechip/Makefile
+++ b/firmware/slavechip/Makefile
@@ -1,5 +1,6 @@
 include ../Makefile.inc
 
+DEFINES += -DF_CPU=8000000
 COMPILE = avr-gcc $(CFLAGS) $(DEFINES)
 
 OBJECTS = main.o mcp_adc.o i2c_simple.o softtimer.o spi_proto.o spi.o spi_pointers.o muxer.o debug.o
diff --git a/firmware/slavechip/muxer.c b/firmware/slavechip/muxer.c
index 4dbe6f7..39c3a3d 100644
--- a/firmware/slavechip/muxer.c
+++ b/firmware/slavechip/muxer.c
@@ -17,16 +17,16 @@ void muxer_set(uint8_t channel){
 
 void offset_measure_init(){
 	DDRD |= 0x0f; // first 4 pins as output
-	PORTD = 0x00; // turn everything off
+//	PORTD = 0x00; // turn everything off
 }
 
 void offset_measure_start(uint8_t channel){
 	if(channel >3){
 		return;
 	}
-	PORTD = (1<<channel);
+	PORTD |= (1<<channel);
 }
 
 void offset_measure_stop(){
-	PORTD = 0;
+	PORTD &= ~0x0f;
 }