Oki has this on their support site and we had similar problems as
described until we found this solution. I'm attempting to paste the
content into my reply here.

Doc #: 2057 Category: General Last Updated: 01/19/2001

How To:
Configure the HP Jet Direct Devices to the 300 series Turbo Printers.

The following steps are necessary for configuring Hewlett-Packard Jet
Direct EX (external) devices.
This doent will apply to HP Jet Direct device models EX, EX+,EX+3,and
EX+3/100VG. The HP Jet Direct
devices come with software to setup the parallel port. This doent
applies to software version 2.33. Other
versions will have the same settings to change, but may have different
menus to get to those settings.
Additional questions should be referred to HP.

The HP Jet Direct software should be configured for "Interview Mode."

1. Connect the Okidata printer to the Jet Direct External Device using a
1284 - IEEE compliant bi-directional cable.

2. Power on the printer and the HP Jet Direct device.

3. If you have not previously configured the Jet Direct device, look at
the bottom of the Jet Direct device for a label
containing the product's address (08000 ...,006...).

4. Run the HP Jet Admin Software configuration tool.

5. If you have already configured the Jet Direct device you should see
it listed on the main screen within Jet Admin.
(if you do not see it then go to "Device" then "New" and select it from
the list. Follow the steps listed until you reach
the "Optional" screen. Proceed to step #8).

6. Using the right mouse button, click on the printer and scroll down
to modify.

7. Now click on "Next" until you reach the "Optional" tab.

8. Click the down arrow beside "Parallel Mode: Speed of Connection" and
select "Centronics".

9. Next, click the down arrow beside the "Parallel Handshaking:
Communication Protocol" option.
Select "nACK and Busy".

10. Click "finish". Shortly after, a box will appear indicating that the
configuration is saved.

11. You must now power-cycle (power off/on) the printer for these new
changes to take effect.

NOTE: This setup should work with the factory default settings of the
Okidata ML320/1 Turbo,
ML390/391 Turbo printers.

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