The configurable 48-bit up/down counter iC-MD is designed for the easy connection of fast incremental encoders, enabling count frequencies of up to 40 MHz. The integrated direction discriminator detects the direction of movement and moves the counter up or down with each edge at the A and B inputs.
iC-MD has three input channels that can be used as differential RS422 or LVDS receivers for ABZ signals. Alternatively, three AB signal pairs with TTL levels can be processed at the six inputs. The 48-bit up/down counter can be configured as a 16, 24, 32, or 48-bit counter with differential RS422/LVDS input signals. With incremental AB encoders with TTL signal levels, up to three measuring instruments with a counter depth of 16 bits apiece can be evaluated. If only two measuring devices are connected up, either both AB encoders can be evaluated with 24 bits each or one with 16 bits and the other with 32 bits.
iC-MD is activated and programmed either via an SPI by a microprocessor or via the serial BiSS interface. iC-MD can also act as a BiSS slave interface device so that existing microcontroller-based sensors can be extended to include the real-time-competent BiSS interface. Typical applications are:
An additional 24-bit counter has been implemented to measure the distance between two Z pulses. An external event can also operate the edge-activated TPI input and trigger temporary storage of the counter reading, either with the positive or negative edge.
The phase length of the AB signals and the supply voltage are monitored to detect any errors. In the event of error a low active is signaled at NERR. If the up/down counter overshoots or undershoots, a low active warning is reported at the NWARN output to the microprocessor. Both message outputs are of the open collector type and can act as an interrupt message for the microprocessor in wired-or circuitry.
The iC-MD device can be used to directly process distance-coded reference marks. Using the numerical relationship of two position distances between three reference marks, the absolute position of the system can be determined with little effort and reduced movement. Using iC-MD and by adding several reference marks, a basic incremental system can thus be extended to form a semi-absolute system. The use of such distance-coded absolute systems is preferred with linear, cost-sensitive measuring systems.
An evaluation board entitled iC-MD EVAL MD1D is available for the evaluation of iC-MD. The PC operating software, available as a free download, can directly access the evaluation board via a PC adapter (USB on an SPI).
iC-MD operates with a supply voltage of 3.3 V to 5 V and comes in a 6 mm x 9 mm TSSOP20 package. The operating temperature ranges from -40°C to +125°C.