COMPARING HIGH-DENSITY AND 4-CHANNEL DIGITAL MODULES
SNAP High-Density Digital Module User’s Guide
12
what it already has for each point. Update time varies based on the number of modules on the rack and
Ethernet communication demands placed on the processor.
Counting speed for high-density digital modules is up to 50 Hz at a 50% duty cycle. This rate is useful for
applications that require counting at lower speeds—for example, rotating shafts, flow meters that generate
pulses, and electrical meters tuned to slower speeds.
Because counting is done in the module rather than in the processor, you can get counts for HDD modules
used with SNAP-PAC-R2 controllers and SNAP-PAC-EB2 and SNAP-PAC-SB2 brains—processors that don’t have
high-speed counting capability.
Use in PAC Control
In PAC Control,
1-series processors
(SNAP-PAC-R1, SNAP-PAC-EB1, and SNAP-PAC-SB1, including -FM and -W
models, and the SNAP-PAC-R1-B) configure and use high-density digital modules much like 4-channel digital
modules. However, because of the differences in counters shown in the table above, only the commands Get
Counter, Get & Clear Counter, and Clear Counter will have an effect. Since counting is automatic and
continuous on the high-density module, be sure you clear the counter each time before starting to use it, so
you know it’s starting from zero.
Because PAC Control does not allow counting on
2-series processors
(SNAP-PAC-R2, SNAP-PAC-EB2, and
SNAP-PAC-SB2, plus their -FM and -W models), you cannot configure points on HDD modules as counters.
However, you can work around this limitation by simply enabling and using the legacy HDD module
commands: Get HDD Module Counters, Get & Clear HDD Module Counter, and Get & Clear HDD Module
Counters. See the
PAC Control User’s Guide
for instructions to enable legacy commands. Remember to clear the
counter each time before starting to use it, since counting is continuous.
If you not using SNAP PAC brains and controllers but are using older hardware, see
4-Channel Digital Counting
High-density Digital Counting
Counters must be started.
Counters can be:
•
Started
•
Stopped
•
Read
•
Read & Cleared
Counting is supported on 1-series processors only
(R1, EB1, SB1).
Counters are always counting.
Counters can be:
•
Read
•
Read & Cleared
Counters cannot be started or stopped.
Counting is done on the module.
HDD input counting is supported on all processors
(R1, R2, EB1, EB2, SB1, SB2)
