Specifications

E–4 Principles of Operation
Communicating with the Host Computer
The CCB processes three kinds of computer input: Centronics parallel,
DataProducts parallel, and RS–232 serial data. The RTPU operates all three
interfaces. The parallel interfaces are similar, and the RTPU contains
direct–memory–access (DMA) hardware which loads parallel data directly
into shared memory. The serial interface requires byte–by–byte intervention
by the processor, since ACK/NACK and XON/XOFF protocols require that
every byte be examined as it is received. The universal asynchronous
receiver/transmitter (UART) is internal to the RTPU, which processes any
protocol requirements then puts the data in shared memory, where the DPU
can read it. To the DPU, all input data looks the same, regardless of the
interface used to receive it.
Communicating with the Operator
All communication to and from the operator is done at the operator control
panel. The control panel processes three types of operation: keystroke input,
message display output, and indicator output. The RTPU handles the control
panel interface requirements of shifting, clocking, etc., but the DPU
processes all control panel data.
Printing
The RTPU coordinates printing of the dot images sent from the DPU.
Printing is a complex process requiring many control functions, but is
logically divided into two groups:
• Hammer driver interface functions
• Mechanical interface functions
Hammer Driver Interface
In order to print a dot image, two things must happen. First, the dots must get
to the hammers one dot row at a time and in the correct sequence. Second,
the hammers must be fired at the appropriate time in the stroke of the shuttle.
The RTPU microprocessor controls both of these functions, but each is
actually performed by an application–specific integrated circuit (ASIC)
containing hardware dedicated to the function. These ASICs are the Dot
Plucker Memory Controller (DPMC) and the Fire Timer IC (FTIC). The
hammer driver interface functions of the RTPU are summarized in
Figure E–3.