Gamry ECM8, Operator'S Manual

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Chapter 2 -- Introduction--Communications Overview
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should be less than 0.2  . A good ZRA is much better in this regard, with electrode-to-electrode
impedances in the low m  .
Communications Overview
The system computer communicates with the ECM8 via an RS232 connection. RS232 is a very popular
serial communications standard. Often computer manufacturers refer to RS232 ports simply as serial ports.
In the world of IBM compatible computers, RS232 ports are known as COM ports. Windows, as a result of
its MS-DOS heritage, supports 4 to 8 COM ports, addressed as COM1 through COM4 (or COM8).
If your computer does not include any COM ports, you can often still use it with an ECM8. PCI plug-in
cards with RS232 ports are available. In addition, USB to RS232 converters that mimic the operation of a
COM port are also quite common. Contact Gamry ’ s technical support staff or your local Gamry
representative if you need help identifying an appropriate RS232 solution.
This manual refers to RS232 ports and connections when discussing ECM8 communications that are
computer independent. It refers to COM ports when the discussion is specific to Windows computers.
RS232 communications can occur at various speeds, called baud rates. Both of the devices connected by
an RS232 connection must be set for the same baud rate. The ECM8 is factory set for 9600 baud, which
should prove adequate for most applications. At 9600 baud, an RS232 link transmits one 8 bit character
roughly every millisecond. Gamry ’ s Framework applications all use 9600 baud as their default baud rate.
You can change the ECM8 baud rate using a DIP switch on the ECM8 printed circuit board. Appendix B
contains a list of the available baud rates and detailed instructions on changing the baud rate switch.
Warning
Always unplug the ECM8 power cord before opening the ECM8 chassis.
Dangerous voltages are exposed in the ECM8 with its top cover removed.
Consult your computer manual for instructions on changing your computer's baud rate. Modern computers
set the baud rate in software so it is generally easier to change your computer's baud rate to 9600 baud
rather than change the ECM8 baud rate.
RS232 communications have several other parameters that must be set correctly to insure proper
communications. Both communicating devices must be set for the same number of data bits, stop bits, and
parity. The ECM8's communication parameters are fixed at 8 data bits, one stop bit and no parity. Your
computer's communication parameters should be set to the same values.
All RS232 communications to the ECM8 are done via the exchange of ASCII characters. Appendix D
describes the command formats. If you use the Gamry Framework to control your ECM8, you can ignore
all this detail.
RS232 cabling is unfortunately not very well standardized. You can find the pin-out of the ECM8's RS232
connector in Appendix C. The ECM8's RS232 port has been wired as an RS232 DCE (data
communications element), similar to a modem. Your computer's RS232 port is normally wired as a DTE
(data terminal element). In most cases, an RS232 cable that connects a modem to your computer will
successfully connect the ECM8 to your computer.
The ECM8 comes with an RS232 cable suitable for connection of an ECM8 to the 9 pin COM port on an
IBM AT compatible computer. If you need to connect the ECM8 to a 25 pin COM port, you can use this
cable with a 25 to 9 pin adapter. These adapters are inexpensive and available at most computer retailers.