usb serial port intermittent problem with hp laserjet 4plus


I am using your USB Serial Converter to communicate between my W7 machine and a HP LaserJet 4 Plus. It works fine except that after printing 15 pages or so, the printer returns an Error 40 which indicates a communication baud rate, parity, flow control etc problem.

Baud is set to 56k
Parity is none
1 stop bit
DTR flow control is on


Chet Smith


Hi Chet,

Thanks for posting! We’ll try to help.

As you know, serial communication is more fragile than most of us are used to (compared to network or USB transfers).

A few questions and things to try:

How long is the serial cable between our adapter and the LaserJet printer? Do you have a shorter cable to try?

Also, is the LaserJet’s baud rate configurable? Are you able to drop to 28.8K or 9600 on both sides of the connection (at least temporarily) to see if the data rate is interacting with a noisy line?

Thanks and best wishes,