Allen Tel Products ATMT25-MF RS232 Male To Female Mini-Tester

this is a mini Fester it's used in troubleshooting and establishing serial connectivity the important thing about many testers that has defeated light in the r d-- light for a serial connection to work we need to have pd on one side and rd on the other side it doesn't matter which is which but we need one on one side and the other on the other so that when you put them together you get both TD and RD if you plug in your connection on one side and you have either TD or Rd and then you plug in on the other side and have the same and what you need to do is introduce a null modem what a null modem does is it flips pins 2 & 3 pens 2 & 3 are used for transmit and receive data so they went to introduced its swaps so we have already lied on now with the null and if we remove the yard the null modem will have feeding