Command register (base address + 13)

This write-only register allows the software to control the AC3. Functions are commanded by writing a ‘1’ to the appropriate bit. When a ‘0’ is written to a bit, nothing happens. This allows the software to control individual functions by writing to selected bits with a ‘1’, while leaving the other bits set to ‘0’. The command bits are shown below:

Bits 15 to 12 - Not used

Bit 11 - ACQUIRE data and latch timer count

• Writing a ‘1’ to this bit causes the AC3 to acquire the SP25M axis deflections and latch the time stamp. The data is presented in registers ‘5’ to ‘0’, and the time stamp is latched into registers ‘7’ and ‘6’. While the data acquisitions process takes place, its progress can be monitored by inspecting the BUSY bit in the status register. Writing a ‘1’ to bit 11 can take place in any of the AC3 operating modes and will result in data acquisition.

Bit 10 - REQUEST SET PROBE PRESENT

• Writing a ‘1’ to this bit causes the AC3 to sample the state of its probe identification circuitry. Upon writing to this bit, the PROBE PRESENT bit in the status register is set to ‘1’ if an SP25M probe is present.

Bit 9 - REQUEST RESET OVER-RANGE

• Writing ‘1’ to this bit causes the AC3 to sample the state of its over-range circuitry. Upon writing to this bit, the OVER-RANGE bit in the status register is set to ‘0’.

Bit 8 - RESET TIMER

• Writing a ‘1’ to this bit causes the AC3 to reset the AC3 timer to 0000H and resets the TIMER OVERFLOW flag to ‘0’.