PC ORG @ 0x1e + ! ( chkPS )
    HL PUSHqq,
( We have the return address for this very call on the stack
  and protected registers. 4 - is to compensate that. )
    HL PS_ADDR 4 - LDddnn,
    SP SUBHLss,
    HL POPqq,
    CNC RETcc,      ( PS_ADDR >= SP? good )
    JR, L2 BWR      ( abortUnderflow-B298 )