Measurement Computing USB-QUAD08 - Manual (Page 19)

USB-QUAD08 User's Guide Functional Details
19
37-pin connectors (J12, J50)
The USB-QUAD08 has two 37-pin D-type connectors (J12 and J50). Each connector provides Phase A, B, and
Index connections for up to four quadrature encoder inputs. Connector pinouts are shown 12.
Connector J12 is on the right side of the device (as shown in Figure 15 on page 18). Connector J50 is internal;
you must remove the board from the housing to access connector J50.
LED indicators
The USB-QUAD08 has LEDs for power and communication status (see Figure 16). Additionally, each
encoder/counter channel has an associated status LED adjacent to its screw terminal bank (see Figure 2
on page 8.)

Power LED: indicates that the device microcontroller has power and is running.

Status LED: indicates that the USB is configured; blinks to indicate USB traffic.

Channel LEDs: indicates that the encoder/counter is receiving a valid signal on any of the inputs
USB connector
The USB connector provides +5 V power and communication.
Counter input modes
The USB-QUAD08 supports the following counter input modes:
 Counter – Quadrature or Totalize mode
 Period measurement
 Pulse-width measurement
Counter operation modes are programmable with software. Some modes make use of a user-configurable value
called the MAXLIMIT value. This value doesn’t directly affect the current count, but sets a limit used in some
modes to determine counter behavior.
All counter modes use the phase A input. Some modes also make use of the phase B and Index inputs.
Each mode supports additional sub-modes for counter operations. Refer to the discussion of each counter mode
in the pages that follow for specific information.
Quadrature counter mode
The USB-QUAD08 can simultaneously decode signals from up to eight encoders. Quadrature encoders with
16-bit, 32-bit, or 48-bit counters, 10 MHz maximum pulse frequency, and X1, X2, and X4 count modes are
supported.
The USB-QUAD08 provides Phase A (±), Phase B (±), and Index (±) inputs for each encoder connected (0 ,
90 , and zero). Phase A and Phase B are generated at a 90° phase shift with respect to each other. Phase A and
B signals are used to determine system position (counts), velocity (counts per second), and direction of rotation.
The Index signal can be programmed to gate, latch the current count, decrement, or clear/reload the counter
with the MAXLIMIT value.
The Index signal may be used to establish an absolute reference position within one count of the encoder
rotation (360°). This signal can be used to reload the position counter, which is useful at system startup when
the incremental encoder cannot determine the starting position of the motor.
The Terminal count / MAXLIMIT status can be output to the DIO terminals.
Each input can be debounced from 500 ns to 25.5 ms (total of 16 selections) to eliminate extraneous noise, or to
switch induced transients. Encoder input signals must be within –12 V to +12 V, and the switching threshold is
200 mV differential or 200 mV above 3.0 V and 50 mV, typical, hysteresis. Refer to page 22 for additional
information about Debounce mode.