System Terminology; Communications Register Unit (Cru) - Texas Instruments 990 Installation And Operation Manual

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945423-9701
135978 (911-477-39-3)
Figure 1-1. Model 911 Video Display Tenninal
Optional components available for the Model 911 VDT include:
• Extension cable assembly, Part Number 946093
• Extension cable kit, Part Number 936503
1.2 SYSTEM TERMINOLOGY
Figure 1-3 illustrates the relationship of the major components of the VDT system. The
following paragraphs describe the function of each of the components to provide an understand-
ing of system operation.
1.2.1 COMMUNICATIONS REGISTER UNIT (CRU). The Communications Register Unit
(CRU) is the serial interface of the Texas Instruments Model 990 Computer. Data is transmitted
between the controller and the computer through this interface one bit at a time (each character
on the keyboard generates eight data bits). This transfer occurs so rapidly that no delay is
apparent to the operator. Status from the controller and control information from the computer
also use this interface.
1.2.2 VDT CONTROLLER. The Model 911 VDT Controller is implemented on a full-size
printed wiring board that fits into one of the chassis locations of a Model 990 family computer
or a Model990 family computer expansion chassis. Depending on the selected option, the
controller is actually one or two autonomous controllers that share a common CRU interface
and time-base generator.
The controller receives data from the computer and the terminal keyboard and stores screen
symbol data in a self-contained display-image memory. The controller reads the data from its
memory and generates a signal pattern to write that data onto the VDT screen. Data is
continually rewritten on the screen for image refresh.
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Digital Systems Division