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Principles of Operation
transfer is achieved by having hardware shift the DMA addresses by one
bit—effectively multiplying the address by two and changing the DMA’s
auto–increment from byte to word. Software adjusts the addresses provided
to the DMA controller when it is programmed for sixteen bit DMA. This
manipulation saves the cost of a separate sixteen bit DMA controller and
eliminates the extra cycle that would be required if the Z8S180 eight bit
DMA were used without this modification.
Host Serial Input Serial communication with the host is done with an
external ST16C2450 dual asynchronous receiver/transmitter (DUART).
Communicating With the Operator
Control Panel
The synchronous serial port in the Z8S180 shifts data in and
out of the operator control panel. The control register in the RTPU contains
three other control panel bits: one samples the switches, one strobes the
liquid–crystal display, and one strobes a light–emitting diode (LED) holding
register.
Diagnostic UART The LMI interfaces with an external diagnostic RS–232
modem. Diagnostic interface communication is done on channel B of the
ST16C2450 DUART.
Floppy Disk Controller Module The LMI has an on–board floppy disk
controller module that occupies virtual slot 1 on the Printronix bus.
Printing
Hammer Driver Interface
Dot plucking is handled by the Dot Plucker ASIC
(DPMC), which runs at 20 or 32 MHz using the RTPU input clock. The
Z8S180 programs the dot plucker ASIC and the FTIC on every dot row, after
which the FTIC uses a DMA request line to control the movement of tables
from EPROM to FTIC. The second DMA controller in the Z8S180 performs
this transfer.
Mechanism Driver Interface The paper feed controller (PFC) directs all
paper motion. During printing, it usually moves paper in response to a trigger
from the FTIC, which synchronizes paper motion with shuttle motion. The
Z8S180 programs the PFC 8032 through an eight bit parallel port between
processors at the beginning of each dot row, telling the PFC how far to move
when the trigger is received. The PFC sets up for the move, waits, then
moves when the trigger occurs. The other method of starting paper motion is
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