SA3_APWRDWN
ym_write(sc, SA3_APWRDWN,
ym_read(sc, SA3_APWRDWN) | (parts >> 8));
ym_read(sc, SA3_APWRDWN) & ~(parts >> 8));
ym_write(sc, SA3_APWRDWN, apd);