( Z80 driver for TMS9918. Implements grid protocol. Requires
TMS_CTLPORT, TMS_DATAPORT and ~FNT from the Font compiler at
B520. Load range B470-472 )
CODE _ctl ( a -- sends LSB then MSB )
    HL POP, chkPS,
    A L LDrr, TMS_CTLPORT OUTiA,
    A H LDrr, TMS_CTLPORT OUTiA,
;CODE
CODE _data
    HL POP, chkPS,
    A L LDrr, TMS_DATAPORT OUTiA,
;CODE