100321-1056 EST
I want to try to clarify some points about the question from a general perspective.
I know nothing about the Edwards system. Or what EST-3 FACP is.
It appears from the comments that Edwards has an RS232 connection for sending data from it to an external device.
RS232 is basically a serial communication standard for signal levels, impedances, and current limiting. There are many variations on the basic standard and different implementations. At times there are compatibility problems.
Fundamentally RS232 communications it is means of transferring binary data in a serial sequence on a wire pair. Wire pair because you need a closed path. There is a separate wire pair for transmitted data and received data. This is an unbalanced transmission system as distinguished from RS422 and 485. Unbalanced means the signal is measured between a data line and a common line. The common line is usually connected to ground (earth). The common of the transmit and receive signals is shared so only 3 wires are required to supply the two wire pairs. RS422 requires 4 wires and maybe a common as well. In a balanced system as distinguished from an unbalanced system a voltage difference is measured between two signal wires. In the unbalanced system the signal voltage is measured from common (ground) to a signal line. An unbalanced system is more susceptible to ground path noise than is a balanced system.
In a normal RS232 system the open circuit voltage swings from a + to a - value. The rest state is a logical 1 and is a negative voltage. On an IBM male 9 pin chassis connector this output is on pin 3. Pin 2 is the receive signal, and pin 5 is the signal common, also connected to the computer chassis. Originally the RS232 values were 12 or 15 V, now in many cases about 5 V. There is an intended dead band around 0 where the signal is undefined. This aspect is not well adhered to by some receivers or even some transmitters.
For communication to take place between two points the transmitter of one must connect to the receiver of the other. Often times these are labeled as TxD and RxD.
There are some additional handshaking signals that exist in the standard, but these are not required for basic communication. Basic communication can be performed with just three wires TxD to an RxD, RxD from a TxD, and common.
Since in the post by fvilla flow control is listed as none it is quite likely that the handshake pins can be ignored.
How do you verify a three wire connection from one device to another?
If you have no specific information, then on a 25 pin connector assume that pin 7 is common, and on a 9 pin it is pin 5. Two tests to verify this assumption. With power off use an ohmmeter to check resistance from pin 7 or 5 to the chassis. If the resistance is under about 100 ohms, then the assumption is probably correct. With power on the DC voltage from the common pin to ground (chassis) should be very close to 0.
In general pins 2 and 3 are the transmit and receive pins. With power on and no data being transmitted the TxD pin should be more negative than -5 V. The RxD pin usually shows a small offset from 0, like maybe 0.16 V. When you identify which pins are the TxD pins, then make up or use a commercial cable that provides the necessary connections. For instance in connecting a HAAS CNC machine 25 pin to IBM 9 pin connector pin 2 goes to pin 2, pin 3 to pin 3, and pin 7 to 5.
The above is the hardware aspect. You always need to match baud rates at each end. The transmitting end can be set to one or two stop bits. Standard UARTs always use one stop bit for receive. In most applications both ends must be set to the same number of data bits, and along with this parity must correspond. There are some rare cases where parity is checked somewhere else than in the UART and then there is a disparity in these settings. I have to assume that these various parameters provided by fvilla are what you should use.
Now we get to communication protocol. From fvilla's comment to use TTY mode this probably means that either the source automatically dumps data to the serial line, or that a button is pushed on the source to initiate data transfer, or you type some command on the keyboard of the receiver to initiate the data dump. Given that this is the protocol, then many plain serial communication programs should work.
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