HMC7000 Series I/O Module Guide
78
HMC7000 Series I/O Module Guide
78
Note: arrow indicates current flow direction
In order to have current flow, each I/O terminal on the expansion module must have a return path or a
signal ground connection. In most modules, multiple I/O terminals share the signal ground connection.
Digital Outputs (PNP or NPN type)
The output terminals of a digital I/O module use an optically isolated PNP or NPN transistor to energize
the connected load. PNP/NPN outputs are faster than relay outputs but can only work with low current
DC loads (typically 500mA max per terminal). PNP modules are sourcing modules, and NPN modules
are sinking modules.
PNP-type connection (Source)
NPN-type connection (Sink)
Note: the above diagrams show that a PNP output is ‘sourcing’ current and the NPN output is ‘sinking’
current.
