Line turn circuit for data link

In a network wherein a main host computer communicates to a train printer peripheral unit via an I/O subsystem having a plurality of peripheral-controllers housed in a base module, said base module having a backplane connection means for slide-in connection of cards holding a plurality of peripheral-controllers and a maintenance card checking means, and foreplane connection means, wherein each of said peripheral-controllers is made of a common-front-end circuit card and a peripheral dependent board card linked by said foreplane connection means, the combination comprising:

• (a) a distribution control circuit card connected to said backplane connection means of said base module, said distribution control circuit card including:
• (a1) bus connection means to said main host computer;
• (a2) logic means, responsive to said main host computer or one of said peripheral controllers, to connect or disconnect said main host computer with a selected peripheral-controller;
• (b) a train-printer peripheral-controller connected to said backplane connection means, said train printer peripheral-controller including:
• (b1) receiver circuit means for enabling data flow from said main host computer, via said backplane and distribution control circuit card, or enabling data flow from said maintenance card checking means, via data bus connection means, to memory storage means in said peripheral-controller;
• (b2) data-driver transmit circuit means for enabling data flow from said memory storage means to said distribution control circuit card for transfer to said main host computer or for transfer to said maintenance card checking means;
• (b3) data bus line connection means between said distribution control circuit card and said memory storage means in said train-printer peripheral-controller;
• (b4) memory storage means for storing data to be transferred for operation and control of said train-printer peripheral unit, said memory storage means being connected to said data bus line connection means for receipt of data and for output of data;
• (c) directional flow control means, initiated by said train-printer peripheral-controller, controlling said receiver circuit means and data-driver transmit circuit means for selecting data transfer flows either from said memory storage means in said train-printer peripheral-controller to said distribution control circuit card, or from said distribution control circuit card to said memory storage means in said train-printer peripheral-controller.