IBM RT PC Options Installation page 211

The illustration above shows the normal Switch Bank 1
configuration. Use the following table to set Switch Bank 1 if your
configuration requirements differ.
Note: If you are using the IBM Monochrome Display and Printer
Adapter in conjunction with the Megapel adapter, the printer port
on the Megapel adapter must be disabled or a conflict will exist on
Interrupt Level 7. Refer to "Adapter Conflicts" on page 1-19 and to
the Interrupt and Usage Table on page 1-21 and 1-22.
If you have a Color Graphics Adapter (CGA) or an adapter that
emulates CGA (EGA, for instance) Switch 3 of Switch Bank 1 must
be set to OFF.
Switch Function
1 Reserved; must be Off
2 Printer Port
3 Color Graphics
Emulation
4 Reserved; must be On
Installing: The Megapel Adapter requires two adjacent, long
adapter slots. Slots 4 and 5 in the IBM 6150 and slots 2 and 3, 3 and
4, or 4 and 5 in the IBM 6151 can be used.
See the system unit diagram to locate the adapter slots.
Off
Disable Enable
Disable Enable
Section 7. Display Adapter Options
On
7-19