PCF_SET_S0
#define dummy_write(pcf) PCF_SET_S0(pcf, 0)
PCF_SET_S0(pcf, slave);
PCF_SET_S0(pcf, slave);
PCF_SET_S0(pcf, data);
PCF_SET_S0(pcf, data);
PCF_SET_S0(pcf, pcf->pcf_addr >> 1);
PCF_SET_S0(pcf, 0x1b);
PCF_SET_S0(pcf, 0x19);
PCF_SET_S0(pcf, 0x18);
PCF_SET_S0(pcf, *buf++);