TWS_I2O0_HIMASK
reg = tws_read_reg(sc, TWS_I2O0_HIMASK, 4);
tws_write_reg(sc, TWS_I2O0_HIMASK, TWS_BIT0, 4);
tws_write_reg(sc, TWS_I2O0_HIMASK, ~0, 4);
reg = tws_read_reg(sc, TWS_I2O0_HIMASK, 4);
tws_write_reg(sc, TWS_I2O0_HIMASK, reg, 4);
reg = tws_read_reg(sc, TWS_I2O0_HIMASK, 4);
tws_write_reg(sc, TWS_I2O0_HIMASK, reg, 4);