Page: 40/81 User Manual PSU-CTRL-2D, Rev.1-00: Software Interface
The communication speed of the serial port defaults to 9600 baud but
can be changed to any value up to 230.4 kbaud (see function
). Please note that the highest speed
can be used with any USB connection.
When using the RS-232 interface, check the host hardware for the
maximum available communication speed. Most simple serial ports in
PCs only support communication speeds up to 115.2 or 128 kbaud.
They may also lose data characters when receiving the data from the
device. If you encounter such issues, replace the serial-port hardware
by a high-speed adapter card with a dedicated system driver. USB
adapters providing one or more serial ports usually do not cause any
issues either. However, due to the latency of the USB protocol, they
are significantly slower than serial ports placed directly on a PC main-
board or than serial-port cards.
If a real-time control of the hardware with a temporal resolution of
1 ms or better should be implemented, a high-speed adapter card with
a serial port (RS-232) is the recommended solution. When run at the
communication speed of 230.4 kbaud, a typical command consisting
of 2-3 ASCII characters can be sent within only 0.1-0.2 ms. In contrast
to that, a typical USB transmission may take up to 50 ms. This means
that, usually, only less than 10 bidirectional transfers per second can
be achieved when USB is used.
The communication uses the handshake lines of the serial port. Thus,
when using the RS-232 interface, be sure that you use a connection
cable that connects all pins in the DE-09 (D-Sub-9) connector. The
device emulates a null-modem, i.e. the line DTR is replicated by the
hardware as DSR and DCD and the line RTS is replicated by the
firmware as the signal CTS. If time-consuming tasks like bulk opera-
tions with the NVM are performed, the device deasserts the signal
CTS and indicates that it is not ready to respond. If the host deasserts
the lines DTR and/or RTS, the input communication buffer of the de-
vice is cleared. This can be used to repair the communication if the
response becomes erratic (see function
Moreover, if the lines DTR and/or RTS are deasserted for more than
100 ms, the communication interface is reset and the communication
speed is set to the default value of 9600 baud. This happens auto-
matically when the software stops using the serial port, thus the com-
munication with the device always starts at the default speed of
9600 baud.
CGC Instruments
Tel.: +49 (371) 355 098–55
Hübschmannstr. 18 | D–09112 Chemnitz
Fax: +49 (371) 355 098–60
internet: www.cgc-instruments.com
e–mail: [email protected]
