Using the AC2 card

The AC2, like the AC1, is completely controllable by software. It also contains a 16 byte register set in I/O space that can be accessed starting from the base address selected in section 4.3. The register set is a superset of the AC1’s allowing software for the AC1 to use the AC2 with minimal modification if required. To use the full power of the AC2, will require some changes to existing AC1 software.


The AC2 has the same features as the AC1, but in addition has:

• An optional 16-bit or 8-bit ISA bus interface in I/O space.

• An option to connect to a Delta Tau controller (customer supplied wiring adaptor required)

• X, Y and Z measurement channels with a resolution of 16 bits.

• 6 software selectable operating modes.

• Hardware synchronisation of data acquisition in 5 of the operating modes

• ISA bus interrupt on data acquisition (in mode 3).

• Probe power supply protection with resettable fuses.

• Paged version identification at the AC2 board identification register.

ISA/ Delta Tau bus interface

The AC2 address space is in I/O space when the ISA bus is selected.  Accesses in memory space are not permitted. The bus interface can operate with 8-bit data (bytes) or 16-bit data (words). Selection of the ISA/ ΔT busses, base address and 8/16-bit modes are with selection switches.

X, Y and Z measurement channels

These have 16-bit resolution. Each time the ACQUIRE bit (bit “11” of register “13”) is written to with a “1”, or the appropriate synchronisation hardware is activated, the SP600 axis defl ections are acquired and presented in registers “5” to “0”, and the time latched into registers “7” and “6”.

Integral measurement event timer

This timer has a resolution of 256 microseconds and a maximum value of 16.78 seconds. The timer count register is updated every time the SP600 defl ections are acquired. The timer can be reset to zero when the RESET TIMER bit (bit “8” of register “13”) is written to with a “1”. If the timer reaches its maximum count value of 65536, the TIMER OVERFLOW bit is set to “1”. This can be inspected by reading the AC2 status register (bit “5” if register “14”). The TIMER OVERFLOW bit is reset to “0” when the timer is reset.

Detection of a connected SP600/M/Q

This is carried out automatically by the AC2. When the AC2 recognises that it is connected to an SP600/M/Q probe, it applies power to the probe. Software can inspect whether a probe is fi tted
by fi rst writing a “1” to the REQUEST SET PROBE PRESENT bit (bit “10” of register “13”), then reading the PROBE PRESENT bit will be reset to “0” automatically. This feature is included so that software can detect that a probe has been disconnected, then reconnected since the PROBE PRESENT bit was last inspected.

Probe power supply protection with failure monitoring

The probe power supplies are protected from overcurrent by self resetting fuses (polysilicon current limiting devices) in each supply line. When an overcurrent occurs, the AC2 automatically removes all power from the probe and sets the appropriate OVERCURRENT bit. Software can inspect the status of these bits by reading the AC2 status register (bits “0”, “1” and “2” of register “14”).

Interface for the SP600 overtravel unit

In some applications an SP600 may be fitted with an overtravel unit. Software can inspect whether the probe is not overtravelled by first writing a “1” to the REQUEST RESET OVERTRAVEL bit (bit “9” of register “13”), then reading the OVERTRAVEL STATUS bit in the status register (bit “3” of register “14”). When the SP600 is overtravelled, the OVERTRAVEL bit will be set to “1” automatically.  This feature is included so that software can detect that the probe has been overtravelled momentarily since the OVERTRAVEL bit was last inspected.

AC2 board identification byte

Software is able to read this byte at any time when the page register (“base + 8”) is set to 00H, to confi rm that the adaptor board fitted at the expected base address is indeed AC2. Upon power up, the page register is set to 00H allowing software to read this identification byte without writing to the board.

The AC2 identification byte varies, depending upon the selected bus width of the AC2. When it is in 8-bit mode, the ident is 0CH. In 16-bit mode, the ident is 0BH. Most Renishaw ISA bus adaptor cards have a unique board identification byte at the address “base + 15”.

AC2 board version number bytes

The AC2 is the first Renishaw ISA bus product to have a software readable, hardware version numbering. The HARDWARE VERSION can be read from “base + 15” when the page register (“base + 8”) has been written to with 01H. This number is incremented every time there is a change to the design, whether this is visible to the customer or not.

Often, changes to the hardware are invisible to the customer, such as when a component that is no longer available causes the design to be changed, so changes to the hardware that cause a consequential change to the customer’s software cause the SOFTWARE VERSION number to be incremented.

When the page register has been written to with 02H, the SOFTWARE VERSION number can be read from “base + 15”. The software version is incremented by Renishaw, when a change has been made to the design that requires a change to the customer’s software.