diff --git a/dmx8chan.c b/dmx8chan.c
index 56eeea8..957eb08 100644
--- a/dmx8chan.c
+++ b/dmx8chan.c
@@ -27,53 +27,56 @@
 // channel values
 volatile uint8_t chan[8] = { 0xFF, 0xFE, 0x80, 0x40, 0x20, 0x10, 0x01, 0x00 };
 
-// rx variables
+// rx receive variables
 static uint16_t rx_chan;
 static uint16_t my_base;
 
-// next OCR1 value
+// timer variables
 static uint8_t cnt;
-static uint16_t pwm_load;
+static uint16_t pwm_next;
+static uint8_t out_next;
 
-/*
- * Timer 1 Overflow (every 10ms)
- * - reload 10ms
- * - schedule compare match in 40us
- */
+/* Timer 1 Overflow (every 10ms) */
 ISR(SIG_OVERFLOW1)
 {
 	TCNT1 = TIMER1_RELOAD;
 	OCR1A = (TIMER1_RELOAD + TIMER1_STEP);
-	pwm_load = (TIMER1_RELOAD + (TIMER1_STEP * 2));
+
+	pwm_next = (TIMER1_RELOAD + (TIMER1_STEP * 2));
 	cnt = 0x00;
 }
 
 /*
  * Timer 1 Compare Match (every 40us)
- * - schedule next compare match in 40us
- * - set PWM Outputs (PORTB)
+ * asap:
+ * - schedule next compare match
+ * - set PWM Outputs
+ * interruptible:
+ * - calc next compare match
+ * - calc next output values
  */
 ISR(SIG_OUTPUT_COMPARE1A)
 {
-	OCR1A = pwm_load;
-	pwm_load += TIMER1_STEP;
+	OCR1A = pwm_next;
+	PORTB = out_next;
+
+	/* rest can be interrupted by DMX receive */
+	sei();
+
+	pwm_next += TIMER1_STEP;
+	if (cnt == 0x00)
+		out_next = 0x00;
 
 	cnt--;
 
-	uint8_t out = PORTB;
-	if (cnt == 0xFF)
-		out = 0x00;
-
 	uint8_t i, shift = 1;
-	uint8_t *tmp = chan;
-
+	volatile uint8_t *tmp = chan;
 	for (i = 0; i < 8; i++) {
 		if (*tmp++ >= cnt)
-			out |= shift;
+			out_next |= shift;
 
 		shift <<= 1;
 	}
-	PORTB = out;
 }
 
 /*