Let me try to explain. The two computers you are using have hardware ports that are setup by software.
Each computer is different. One has a Serial Port that has a DB25 Connector and is wired as a DTE.
DTE is Data Terminal Equipment, meaning that the Transmit line is on Pin 2. That is likely your
Osborne, and it's running some Modem software, which uses either a Hardware Handshake or
the XON/OFF Protocol to not overrun the buffer on the receiving computer.
Your PC type computer also has a USB port and has a USB Dongle that creates a Serial port with a
DB9 connector (or DB25 Connector). That DB9 connector is likely wired as a DTE also. (versus a DCE
Data Communications Equipment. DCE's are typically things like a printer or Modem, but there is a VERY
loose STANDARD.) And your PC is using some terminal or modem program to control the hardware to
communicate with the Osborne.
But two different guys wrote the software and you have no clue as to how they coded their software, or how they
designed it to work. But you have a method of testing each end to see how it works. So, just follow along.
To test the Osborne's DTE Port, set your Baudrate, BitsperChar, StopBits, and Parity to some setting.
I'll pick 1200, 8, 1, None for this test. Now on the DB25, short Pin 2 (TX) to Pin 3 (RX), Pin 4 (RTS)
to Pin 5 (CTS) and Pin 20 (DTR) to Pin 6 (DSR). This gives you one end of what is called a NULL MODEM
CABLE. Now use your Modem Program (Terminal) to transmit an ASCII Test file out the selected Port.
You should see the lines of ASCII Text scroll up the screen. (Try picking a file that is around 5-10K so
it's large enough to give you some time to test.
If the screen scrolls and displays the complete ASCII TEXT, then remove the Jumper from Pin 20 to Pin 6.
And repeat the test. If everything still works, then you don't need that jumper on this end to be LOOPED
BACK to the Osborne. But it still might need to be sent to the other Computer's Serial Port.
Now remove the Jumper from Pin 4 to Pin 5 and repeat the test. If everything still works, then you don't need
that jumper on this end to be LOOPED BACK to the Osborne. But it still might need to be sent to the other
Computer's Serial Port.
Now, set the PC to the same RS-232C Parameters. Try the PC Computers Software doing the exact same testing,
only use the proper Pins for a DB9 (or the DB25). You should have similar results, so make good notes of what
Jumpers need to be installed and removed for each end.
Finally connect the OSB DB25 TX pin to the PC DB9 RX Pin. Same for the OSB DB25 RTS Pin to the
PC DB9 CTS PIn. Same for the OSB DB25 DTR Pin to the PC DB9 DSR Pin. Same for the PC DB9
RTS Pin to the OSB DB25 CTS Pin. Same for the PC DB9 DTR Pin to the OSB DB25 DSR Pin.
Of course you need the OSB Pin 7 (GND) connected to the PC DB9 Pin GND.
Now, Send the same ASCII File from OSB to PC, and capture it on the PC. Then SAVE the File and view it.
If it's good then transmit it from the PC to the OSB and save it, then View it.
Further testing can be to remove the unnecessary jumpers as needed, but it's not required.
Once you can send a large ASCII file, then you can use the Xmodem Protocol to send the files you need
to the appropriate Computer.
I typically draw out the connections on paper after the initial testing of each computer using the following.
Note that if you are connecting a DTE to DTE you will cross the Lines for TX & RX, RTS & CTS, and
DTR & DSR. Plus you need GND to GND on both ends.
DB25
2 ........TXD ........--> ........Transmit Data
3 ........RXD ........<-- ........Receive Data
4 ........RTS ........--> ........Request to Send
5 ........CTS ........<-- ........Clear to Send
6 ........DSR ........<-- ........Data Set Ready
7 ........GND ........--- .........System Ground
8 ........CD ..........<-- ........Carrier Detect
20 .......DTR .......--> ........Data Terminal Ready
DE9
1 ........DCD ........<-- ........Data Carrier Detect
2 ........RXD ........<-- ........Receive Data
3 ........TXD ........--> ........Transmit Data
4 ........DTR ........--> ........Data Terminal Ready
5 ........GND ........--- ........System Ground
6 ........DSR ........<-- ........Data Set Ready
7 ........RTS ........--> ........Request to Send
8 ........CTS ........<-- ........Clear to Send
9 ........RI ...........<-- ........Ring Indicator
Larry