Motorola 326X V.34 User Manual page 225

Refer also to Figure C-10, which shows pin locations on Modulus 21 backplanes.
Modulus 9s have a similar layout.
Modem A
Pins
Jumpers on
Left Pin Pairs
Figure C-10. Modulus Backplane Pin Locations (Modulus 21 Shown)
In Hong Kong and the United Kingdom, Busy Out backplanes are hard-wired for
Busy Out operation. These backplanes do not use pin jumpers.
Modem B
Pins Modulus 21 Enclosure,
Rear View
Country-Specific Information C-45