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I would like to make RS232c cross cable for used Nikon DP-303. I try to make two cable ( see in my picture ).

Cable A --> try to get data from RS232c --> data show ????????? g ?????? m ?????

Cable B --> try to get data from RS232c --> nothing show

I very confused my cable is correct or not? (pin 20)

please advice to me

Thank you all

enter image description here

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The connection diagram on the upper left of your picture looks like a normal cross-over (null-modem) serial cable for DB-25 connectors.

Compare with the pinout table on e.g. Wikipedia. What we have is:

DB-25 serial crossover
 1  ---  1  ("Frame" / likely the shielding around the cable)
 2  ---  3  Tx -> Rx  
 3  ---  2  Rx -> Tx (data lines crossed)
 4  ---  5  RTS -> CTS
 5  ---  4  CTS -> RTS (control lines crossed)
 6  --- 20  DSR -> DTR
20  ---  6  DTR -> DSR (another set of control lines crossed)
 7  ---  7  GND
 8  ---  8  DCD 

But if you look at the pinout table for the smaller DE-9 connector, you'll see that the pins are not in the same positions. (They can't, obviously, since pins 10-25 don't exist.) For example, there's no separate pin for the protective ground, and 9 is the ring indicator.

If you need to make a crossover cable from DB-25 to DE-9, you'll either have to take into account the different pinouts, or acquire a DB-25<>DE-9 adapter, and then make/acquire a DE-9 crossover cable. Just make sure to find one with all the control lines connected (and you may need to check that they are not connected oddly, there are different variants on how DTR, DSR and DCD relate to each other.)

Of course, there are tables for the DB-25<>DE-9 crossover connection, e.g. here. That one has DCD combined with DSR, but in your diagram, they're separate.

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