IBM has recently upgraded the microcode for IBM 3174 controllers.
Versions 3.0 and 3.1 allow command chaining, an enhancement for
the 3174's that increases throughput.
The increase in speed has caused a problem with the timing within
AppleLine. This problem appears as half displayed screens. The effect
is not dramatic, but it is a nuisance. To refresh the screen, type
Control-C.
Apple is studying compatibility between AppleLine and the new 3174
controller code.