Status register (base register + 14)

This read-only register returns the status of the AC3 card. Status bits are as follows:

Bit 7 - Not used

Bit 6 - BUSY

  • This bit is set to ‘1’ when the AC3 has been commanded to acquire data. It is reset to ‘0’ when the data conversion is complete. This takes approximately 15 μs.

NOTE: The host PC should not attempt to read the probe deflections or the timer value while the BUSY bit is set to ‘1’. Any data read during this period will be invalid.

Bit 5 - TIMER OVERFLOW

  • This bit is set to ‘1’ when the timer has overflowed. It is reset to ‘0’ when the timer has been reset.

Bit 4 - PROBE PRESENT

  • This bit is set to ‘1’ if an SP25M probe has been connected to the AC3 and the REQUEST SET PROBE PRESENT bit has been written to with a ‘1’. If the probe is disconnected from the AC3, then the bit automatically resets to ‘0’.

Bit 3 - OVER-RANGE ERROR

  • This bit is set to ‘1’ if the stylus deflection exceeds the operating range. It is set to zero whilst the stylus deflection is within the operating range and the REQUEST RESET OVER-RANGE bit has been written to with a ‘1’.

Bit 2, 1 and 0 - OVERCURRENT STATUS FLAGS

  • These show the status of the three probe output overcurrent protection devices on the AC3. They are set to ‘1’ when one of the probe supplies has had an overcurrent.