Xerox 4215 Reference Manual page 223

HELPFUL HINTS
To resolve the problem, set the Communications Priority Scheme
for the twinax/coax interface on the printer to anything other
than Sequential (which is the default). Other valid options are
Priority, SequentialLock, or PriorityLock. Any of these settings
will ensure that the printer will not look at the next port until
after the coax or twinax job has completed. This prevents the
printer from locking up.
On the 4215/MRP and 4219/MRP control panel, the twinax/coax
interface is referred to as 'Other I/O.' On the 4220/MRP, the
interface is referred to as '4220/MRP Interface.' And on the
4230/MRP, the interface is referred to as '4230/MRP Interface.
XEROX MRP FAMILY COAX COMMAND REFERENCE F-3