A utility function, modemLoopback determines the state of registers and generates an interrupt in the event of modem loopback being requested (a bit in the modem control register). It is used by the busRead and busWrite functions.

Three utility functions are provided to handle interrupts. setIntrFlags sets the interrupt indication register according to which interrupts are currently pending. genIntr generates an interrupt and clrIntr clears an interrupt. In this implementation these functions ensure all register flags are set correctly but do not drive an external interrupt signal.

A set of convenience utilities are provided to set and clear flags in registers (set and clear) and to test the state of a flag bit in a register (isSet and isClear).