IOX

IOX instruction is used for programmed IO. IOX is a privileged instruction in normal cases but if there is no OS running and the paging system is turned off then IOX is an unprivileged instruction. IOX and IOXT are the only instructions used to communicate with external instructions.

IOX transfers data between a device I/O register and the CPU's A register.

Bit 0-10 of the instruction code sets the direction and IO address. If bit 0 is zero then IOX reads the value from the IO register into register A. If bit 0 is one then IOX writes the contents of register A to the IO register.

Addressing of a non existing device results in a IOX error.

See also Programmed IO and IOXT instruction
Ref. Programmed I/O, chapter 6.3 ND-100 Functional Description