Measurement Computing LGR-5320 Series - Manual (Page 22)

LGR-5320 Series User's Guide Functional Details
22
Counter input
LGR-5320 Series devices can read counter inputs as part of a digital scan group.
When read as part of a scan, the count of each channel counter is set to 0 and latched at the beginning of the
acquisition. Each clock pulse (start-of-scan signal) initiates a scan of all channels specified. Each time a
LGR-5320 Series devices receives a start-of-scan signal, the counter values are latched and are available to the
device. The values returned during scan period 1 are always zero. The values returned during scan period 2
reflect what happened during scan period 1. The scan period defines the timing resolution. To achieve a higher
timing resolution, shorten the scan period.
LGR-5320 Series devices support the following counter input modes:
 Counter (general event counting)
 Period counting
 Pulse width counting
 Edge-to-edge timing
 1X, 2X, and 4X encoder counting.
 Up/down counting
Counter operation modes are programmable with software. Some modes use the user-configurable ModuloN
mode. This number does not 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. The
counter signal names on the LGR-5325 are CTRx, UPDNx and GATEx.
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.
Encoder mode (LGR-5327 and LGR-5329 only)
The LGR-5327 and LGR-5329 can simultaneously decode signals from up to four encoders with 16 or 32-bit
counters and X1, X2, and X4 count modes.
Both of these devices provide Phase A (±), Phase B (±), and Index (±) inputs for each connected encoder (0
°,
90
°, and zero). Phase A and Phase B are generated at a 90° phase shift with respect to each other.
The LGR-5327 and LGR-5329 use Phase A and Phase B signals to determine:
 system position (counts)
 velocity (counts per second)
 direction of rotation (B leading or lagging A)
You can program the Index signal to gate, latch the current count, or clear/reload the counter with the modulo
number.
You can use the Index signal to establish an absolute reference position within one count of the encoder rotation
(360°).
Each input can be debounced from 500 ns to 25.5 ms (total of 16 selections) to eliminate extraneous noise, or
switch induced transients. Encoder input signals must be within ±12 V, and the switching threshold is 200 mV
differential, or 200 mV above 3.0 V and 50 mV
typ
hysteresis. Refer to Debounce mode on page 24 for additional
information.