diff --git a/psg.c b/psg.c
new file mode 100644
index 0000000..f233454
--- /dev/null
+++ b/psg.c
@@ -0,0 +1,171 @@
+#include <msp430g2553.h>
+#include <stdint.h>
+#include <stdlib.h>
+
+#include "psg.h"
+#include "scheduler.h"
+
+
+// based on 3.579545 MHz
+const uint16_t frequencyCodes[8][12] = {
+  { 3420, 3229, 3047, 2876, 2715, 2562, 2419, 2283, 2155, 2034, 1920, 1812 }, 
+  { 1710, 1614, 1524, 1438, 1357, 1281, 1209, 1141, 1077, 1017, 960, 906 }, 
+  { 855, 807, 762, 719, 679, 641, 605, 571, 539, 508, 480, 453 }, 
+  { 428, 404, 381, 360, 339, 320, 302, 285, 269, 254, 240, 226 }, 
+  { 214, 202, 190, 180, 170, 160, 151, 143, 135, 127, 120, 113 }, 
+  { 107, 101, 95, 90, 85, 80, 76, 71, 67, 64, 60, 57 }, 
+  { 53, 50, 48, 45, 42, 40, 38, 36, 34, 32, 30, 28 }, 
+  { 27, 25, 24, 22, 21, 20, 19, 18, 17, 16, 15, 14 }
+};
+
+
+#define ADDR_DATA_REG P2OUT
+#define BUS_CTRL_REG P1OUT
+#define BUS_CTRL_IN_REG P1IN
+#define _CS0 BIT1
+#define _CS1 BIT2
+#define _WE BIT3
+#define READY BIT4
+
+#define CHANNEL_A_PERIOD_ADDR 0
+#define CHANNEL_A_ATTEN_ADDR 1
+#define CHANNEL_B_PERIOD_ADDR 2
+#define CHANNEL_B_ATTEN_ADDR 3
+#define CHANNEL_C_PERIOD_ADDR 4
+#define CHANNEL_C_ATTEN_ADDR 5
+
+#define IGNORE_OCTET 0xff
+
+uint8_t psgAmplitudeShadowValue[3];
+
+static void delay() {
+  asm volatile (
+      "push r12\n"
+      "mov.w #5, r12\n"
+      "loop:\n"
+      "dec.w r12\n"
+      "jnz loop\n"
+      "pop r12\n"
+  );
+}
+
+inline static void WRITE_CYCLE(uint8_t chipNo) {
+  if (chipNo == 0) {
+    BUS_CTRL_REG &= ~_CS0;
+  } else {
+    BUS_CTRL_REG &= ~_CS1;
+  }
+
+  BUS_CTRL_REG &= ~_WE;
+
+  delay();
+
+  while ((BUS_CTRL_IN_REG & READY) == 0);
+
+  BUS_CTRL_REG |= _WE;
+
+  if (chipNo == 0) {
+    BUS_CTRL_REG |= _CS0;
+  } else {
+    BUS_CTRL_REG |= _CS1;
+  }
+
+  delay();
+}
+
+static void psgWrite(uint8_t chipNo, uint8_t value) {
+  ADDR_DATA_REG = value;
+  WRITE_CYCLE(chipNo);
+}
+
+static void psgWriteFrequency(uint8_t channel, uint16_t frequencyCode) {
+  uint8_t chipNo = channel / 3;
+  uint8_t regAddr = (channel % 3) * 2;
+
+  // bit order in frequncyCode and order in octet on data bus are reversed
+  // see datacheat cp. 1 and cp. 6
+  uint8_t firstOctet = 0x01;
+  firstOctet |= ((regAddr & 0x04) > 1);
+  firstOctet |= ((regAddr & 0x02) < 1);
+  firstOctet |= ((regAddr & 0x01) < 3);
+  uint8_t lowerPart = frequencyCode & 0x0f;
+  firstOctet |= ((lowerPart & 0x08) << 1);
+  firstOctet |= ((lowerPart & 0x04) << 3);
+  firstOctet |= ((lowerPart & 0x02) << 5);
+  firstOctet |= ((lowerPart & 0x01) << 7);
+
+  uint8_t secondOctet = 0;
+  uint8_t upperPart = (frequencyCode & 0x03f0) >> 4;
+  secondOctet |= ((upperPart & 0x20) >> 3);
+  secondOctet |= ((upperPart & 0x10) >> 1);
+  secondOctet |= ((upperPart & 0x08) << 1);
+  secondOctet |= ((upperPart & 0x04) << 3);
+  secondOctet |= ((upperPart & 0x02) << 5);
+  secondOctet |= ((upperPart & 0x01) << 7);
+
+  ADDR_DATA_REG = firstOctet;
+  WRITE_CYCLE(chipNo);
+
+  ADDR_DATA_REG = secondOctet;
+  WRITE_CYCLE(chipNo);
+}
+
+void psgAmplitude(uint8_t channel, uint8_t volume) {
+  psgAmplitudeShadowValue[channel] = volume;
+  uint8_t chipNo = channel / 3;
+  uint8_t regAddr = ((channel % 3) * 2) + 1;
+
+  uint8_t attenuation = 15 - volume;
+
+  uint8_t firstOctet = 0x01;
+  firstOctet |= ((regAddr & 0x04) >> 1);
+  firstOctet |= ((regAddr & 0x02) << 1);
+  firstOctet |= ((regAddr & 0x01) << 3);
+  firstOctet |= ((attenuation & 0x01) << 7);
+  firstOctet |= ((attenuation & 0x02) << 5);
+  firstOctet |= ((attenuation & 0x04) << 3);
+  firstOctet |= ((attenuation & 0x08) << 1);
+
+  ADDR_DATA_REG = firstOctet;
+  WRITE_CYCLE(chipNo);
+}
+
+void psgPlayTone(uint8_t channel, uint8_t volume, t_octave octave, t_note note) {
+  if (note == e_Pause) {
+    psgAmplitude(channel, 0);
+  } else {
+//    if (psgAmplitudeShadowValue[channel] == 0) {
+      psgAmplitude(channel, volume);
+//    }
+    psgWriteFrequency(channel, frequencyCodes[octave][note]);
+  }
+}
+
+void psgInit() {
+  // address/data bus
+  P2DIR = 0xff;
+  P2SEL = 0;
+  P2SEL2 = 0;
+
+  // bus control lines
+  //   output:
+  //     BIT1: /CS chip 1
+  //     BIT2: /CS chip 2
+  //     BIT3: /WE
+  //   input:
+  //     BIT4: READY
+  P1DIR |= BIT1 | BIT2 | BIT3;
+  P1DIR &= ~BIT4;
+  // immediately disable all outputs, all are active low
+  P1OUT |= BIT1 | BIT2 | BIT3;
+
+  // shutdown all channels including noise
+  psgWrite(0, 0b11111001);
+  psgWrite(0, 0b11111101);
+  psgWrite(0, 0b11111011);
+  psgWrite(0, 0b11111111);
+
+//  psgPlayTone(0, 5, e_O_3, e_A);
+  psgAmplitude(0, 3);
+}
+
diff --git a/psg.h b/psg.h
new file mode 100644
index 0000000..79bcda9
--- /dev/null
+++ b/psg.h
@@ -0,0 +1,46 @@
+#ifndef _PSG_H_
+#define _PSG_H_
+
+#include <stdint.h>
+
+typedef enum {
+  e_O_1 = 0,
+  e_O_2,
+  e_O_3,
+  e_O_4,
+  e_O_5,
+  e_O_6,
+  e_O_7,
+  e_O_8,
+  e_O_Null
+} t_octave;
+
+typedef enum {
+  e_C = 0,
+  e_Cis,
+  e_D,
+  e_Dis,
+  e_E,
+  e_F,
+  e_Fis,
+  e_G,
+  e_Gis,
+  e_A,
+  e_Ais,
+  e_H,
+  e_Pause,
+  e_Null
+} t_note;
+    
+#define e_Es e_Dis
+#define e_As e_Gis
+#define e_B e_Ais
+
+
+void psgInit();
+
+void psgPlayTone(uint8_t chip, uint8_t channel, uint8_t volume, t_octave octave, t_note note);
+void psgAmplitude(uint8_t chip, uint8_t channel, uint8_t volume);
+
+
+#endif // _PSG_H_