Specifications

2–14
Principles of Operation
DATA PROCESSING
RTPU
REAL–TIME PROCESSING UNIT
UNIT
PROCESSOR
DMA CONTROLLER
DOT PLUCKER
FIRE TIMER
EPROM
SHARED MEMORY
Hammer
Driver
Data
Hammer
Timing
Data
ASIC
ASIC
(DPU)
Figure 2–11. Hammer Driver Interface Functions of the RTPU
Getting Dots to the Hammers Getting dots to the hammers consists of
going into the shared memory and pulling bits out in a given order and
shifting them to the hammer driver at the correct time. This process is called
“dot plucking.” The order in which dots are plucked from memory depends
on the dot density, the number of dots per hammer, the number of hammers
on the hammer bank, the number of phases, and other factors. These factors
are all considered by the RTPU processor as it programs the dot plucker and
the FTIC for each dot row.
Synchronizing Dot Plucking and Hammer Firing Transfer of dots to the
hammer driver must be synchronized with hammer firing. Dots are
transferred to the hammer driver in bursts, serial streams of dots that tell
which hammers will print when their phase is next fired. The bursts are timed
precisely; they must occur neither too early nor too late. Synchronization is
performed by having the FTIC request bursts from the dot plucker. The FTIC
reads the magnetic pick–up unit (MPU) to determine when to request a burst.
The time at which the burst request is made is contained in the fire timing
tables.