Do you have an example of doing a read/write over the serial port in the 2151/30 unit?

The setup of the controller for RS 232 bi-directional communications would be to set up the SERCON setting to Bi-Direction.  All other settings, Baud, Length, Stop bits, parity, address, echo, and format, would all be set according to your needs (setup starts on page 5-9 in the manual).  
NOTE: Once you set it as bi-directional, you would need to send a command to get any data transferred.  
Exception:  In the format setup, if you place a "P" in the last location, then you could trigger a print command with the print button, a remote function connection, or a command over the serial port.  With the print command, the unit would then send out the data based on the format setup.

You would need to insure the CTS line on the Hardy unit is pulled high.
Tying it to the RTS line will not normally work.  We have seen users that did not have voltage available, hooked a 9v battery up between ground and CTS.  This works ok, however, you need to keep in mind that when the battery fails, the communications would stop.


Section 7-12 in the manual starts describing the string of data to make up a command.  The manual shows a command to transfer the gross weight from the unit at address 10.  This would be the command string:
">10 X G CR CK1 CK2 EOT"  
That is "Start character, unit address, space, X, space, G, carriage return, checksum 1, checksum 2, End of Transmission"  
Where:
X is the transmit command,
G is for gross weight

NOTE:  If you send the X command with no sub command, then it will send the data based on the Format setup in the unit.  So if the Format is GN____, then the X command with no sub command will transfer the gross and the net weight back.

The format of the string would be the same basic format, but the command may change depending on what you wish to do, and the sub command would also change.
NOTE:  The checksum should be calculated (formula for this is in the manual), but if the user turns on switch #1 of S2 (internal dip switch), it will cause the unit to ignore the check sum.  The string would still need to have a checksum available, but the unit would ignore it if the checksum is incorrect.

An example of writing a value of 1000 Net to setpoint 1 in the unit would be:
>10 S S 1 1000 N CR CK1 CK2 EOT
The checksum would be calculated on the characters after the > and before the checksum using hex values as:
1          = 31 h
0          = 30 h
Space   = 20 h
S          = 53 h
Spa