Controller Boards - Printronix

P9212 Maintenance Manual

Controller Boards

The printer is controlled by either the Common Controller Board (CCB) or
the Line Matrix Impact (LMI) print engine. These boards control the printer
in very similar ways. The main difference between them is the way operating
system and font information is stored: the CCB gets this information from
PROMs, the LMI loads the information into RAM from floppy disk.
Because these controllers are nearly identical in function, they are discussed
together in this section, and collectively referred to as "the controller board."
Differences are noted as they apply.
The controller board oversees and coordinates all printer functions. It is
functionally two units: the data processing unit (DPU) and the real–time
processing unit (RTPU). The DPU converts all character data into printable
dot images. The DPU is the high–level logical controller of the printer; it is
not involved in real–time or hardware–dependent printer operation. The
RTPU operates the host interfaces, operator control panel, and the print
mechanism. The RTPU also monitors the fault circuitry in the mechanism.
On the CCB, these functions are performed on a single circuit board. The
LMI print engine, however, consists of two circuit boards: a DPU processor
board is "piggy–backed" to the larger LMI main board, which carries many
of the resources the DPU needs. The DPU board can have one of three
different microprocessors. On P9212 printers, the DPU uses the Motorola
68EC030 processor, and is called the 030 processor board. In this chapter,
"LMI" refers to the unit formed by the 030 processor board and the LMI
main board.
The DPU and RTPU communicate by means of shared memory. The DPU
gets host and operator input from buffers in shared memory which are filled
by the RTPU, and returns dot images and operator messages to buffers in
memory which the RTPU empties. Figure 2–12 summarizes the architecture
of the CCB and LMI controllers.
2–16 Principles of Operation