Monoprice 101139 DB25 M/F Null Modem Adapter

The Monoprice 101139 DB25 Null Modem Adapter is a straightforward connectivity tool designed for direct device-to-device communication over parallel ports. By internally crossing the transmit and receive lines — similar in concept to how a crossover Ethernet cable works — the adapter lets two computers or devices talk to each other through their DB25 parallel ports without any modem, network switch, or router in between. The male-to-female gender configuration means it plugs inline between a device's parallel port and a standard parallel cable, keeping the setup clean and simple.

This adapter is firmly a legacy product. DB25 parallel ports have been phased out of consumer computers for over a decade, so its primary audience is users maintaining older systems, industrial equipment with parallel interfaces, or retro computing setups. It is worth noting that the adapter only provides the physical signal crossing — you will still need appropriate software on both ends to establish a data link and transfer files. For anyone working with equipment that still relies on parallel-port communication, the Monoprice 101139 is a low-cost, reliable way to make that direct connection happen.