ECP & EPP Printing Crash


Microsoft has advertised Windows NT as a stable system for corporate users. In fact, they like to make you think it can't be crashed. Applications may cause a protection fault and be terminated, but the system will keep running and other applications will be unaffected, they tell us.

Bull shit!

About a week after I installed my first real-time Windows NT system the customer blue screened it. For those of you that don't know what the blue screen means, when Windows NT encounters a fault way down in the bowels of the system it will generate a system stop. Because the error occurred inside the most trusted OS code running at ring 0, the whole GUI becomes unstable. The only way they have of telling the operator about the error is to put the CRT into text mode and show an error message (which they never write down for you). The screen color is blue with white text, thus - blue screen. Your only option at this point is to reboot the computer and hope the hard disk isn't scrambled.

The system I installed was a critical system for the customer. It keeps track of all their sawmill output and prints tickets for the finished packages of lumber. When this system crashes they can lose production data on thousands of dollars of lumber. Not a very happy story. The computer is on a battery backup, and the battery backup is on a backup generator that kicks in when the power goes off. The computer program is designed to automatically save the data every few minutes, or when you exit it, and will automatically recover the most recent data when restarted.

Well, the customer decided to add some production data together and print a report out. They started printing and everything seemed fine. A little later, blue screen, panic, loss of all data.

I had seen problems similar to this on a Compaq Deskpro system running Windows 95. I found a patch file for LPT.VXD on the Compaq web site that was supposed to cure some printing problems with Windows 95. It seems that the computer would crash while printing the shift report every few days. I was fortunate that this system was only used to access a PLC and the lumber tally was being kept in the PLC. Still it was a problem because there is always the possibility of a disk scramble when there is a crash. The Compaq patch file helped the problem but it still happened about once a week.

Further study of the problem indicated that it was in the ECP/EPP mode parallel port. Most new computers are shipping with this new style printer port. It places a greater stress on the hardware and software because it uses DMA and interrupts when sending data. Some computers allow you to set the printer port mode in the BIOS. Compaq doesn't on the older deskpros. We finally needed to purchase a cheap interface card for the Compaq so we could configure a standard parallel port. Once this was installed, and the on-board parallel port was disabled, the crashing stopped.

Other problems you may see when using the ECP/EPP mode is loss of characters and garbage output. Most older printers can't keep up with the higher speed of the new printer port mode. If you can disable the high speed mode in the BIOS, this will usually solve the problem. In fact, Microsoft has documented this problem in their KBase file for Windows 95. They have not, however, owned up to the problems with crashing. And I mean a big crash. The computer will usually lock up and require a power failure to get it going again.

With this past history in mind, I had the Windows NT customer disable the ECP printer mode and so far there have been no crashes.

© James S. Gibbons 1987-2015