Using the AC1 card

Following installation, the AC1 is completely controllable by software.  It contains a 16 byte register set in I/O space that can be accessed starting from the base address selected in section AC1 software interface.

AC1 Features

The AC1 has the following features:

• 8-bit ISA bus interface in I/O space
• X,Y and Z measurement channels with a resolution of 12 bits
• Integral measurement event timer
• Detection of a connected SP600/M/Q
• Probe power supply protection with failure monitoring
• Interface for the SP600 overtravel unit
• AC1 board identification byte

8 Bit ISA bus interface

The AC1 address space is in I/O space. Accesses in memory space are not permitted. The bus interface operates with 8-bit data (bytes) only. There are no interrupts.

X, Y and Z measurement channels

These have 12-bit resolution. Each time the ACQUIRE bit (bit “11” of register “13”) is written to with a “1”, the SP600 axis deflections are acquired and presented in registers “5” to “0”, and the time is 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”. This can be inspected by reading the AC1 status register (bit “5” of register “14”). The TIMER OVERFLOW bit is reset to “0” when the timer is reset.

Detection of a connected SP600, SP600M or SP600Q

This is carried out automatically by the AC1. When the AC1 recognises that it is connected to a SP600 or 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 in the status register (bit “4” of register “14”). When the SP600 or SP600M is removed, 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 fuses in each supply line. When any of the fuses blow, the AC1 automatically removes all power from the probe and sets the appropriate FUSE BLOWN bit. Software can inspect the status of these bits by reading the AC1 status register (bits “0”, “1”, “2” of register “14”).

CAUTION: If the fuse blows, then the fault that caused the fuse to blow must be corrected, and the fuse must be replaced by one of the same type and rating.

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.

AC1 board identification byte

Software is able to read this byte at any time to confirm that the adaptor board fitted at the expected base address is indeed an AC1. Most Renishaw ISA bus adaptor cards have a unique board identification byte at the address “base + 15”.