Controller Communication With The Host And Operator; Control Panel; Diagnostic Uart (Lmi Models); Floppy Disk Controller Module (Lmi Models) - Printronix

P9212 Maintenance Manual

Controller Communication With the Host Computer and Operator
The controller board 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 look the same, regardless of the
interface used to receive the data.

Control Panel

The RTPU handles the control panel interface requirements of shifting and
clocking control panel data, but it is the DPU that processes the data.

Diagnostic UART (LMI models)

LMI printers are equipped with the "Quad I/O" interface, which contains a
diagnostic universal asynchronous receiver/transmitter (UART) for RS–232
serial input/output to a modem or terminal. This diagnostic tool is controlled
by the RTPU.

Floppy Disk Controller Module (LMI models)

The floppy disk controller module is on the LMI main board; it controls the
flow of DPU program data from a standard 3.5 inch floppy diskette to the
DPU program memory. The DPU controls this floppy drive.

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
2–18 Principles of Operation