4-2 Model 3786 Ultrafine Water-based Condensation Particle Counter
The Serial and USB data interfaces share a common
communications channel to the UWCPC microcontroller. Figure 4-1
provides a diagram of the data communications paths within the
UWCPC. Data input to the UWCPC from the Serial interface is
exclusive from input via the USB interface. Communications can be
received from the Serial interface until a connection is linked to the
USB Port. Once this link is established (USB link light is on)
communications can be received via the USB Port but not from the
Serial port. When the USB link is terminated (disconnected) the
Serial port can be again used to provide input to the UWCPC.
Figure 4-1
UWCPC Data Communications Diagram
The UWCPC can receive serial data commands from the Internal
Com and from either the Serial or the USB Port but not both. The
UWCPC uses a single receive buffer for communications so care
must be taken to ensure that commands are not sent
simultaneously causing the data to be jumbled. This is typically not
a problem as the Internal Com is not used unless a user initiated
program is running on the PC/104 SBC. UWCPC responses to
commands received on the Internal Com are returned on the
Internal Com and commands received from the Serial or USB
interfaces are returned on BOTH of these interfaces.
UWCPC Communications Diagram
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