Specifications

2–19
Principles of Operation
Communicating with the Host Computer
The 64180 processor runs both the parallel and serial interfaces.
Parallel Input Parallel input data is nine bits wide, and is transferred in one
cycle from the parallel port to shared memory over the shared sixteen bit bus.
Using the internal DMA controller of the 64180 to transfer parallel data
requires some manipulation. The eight bit DMA controller in the 64180
performs either eight or sixteen bit DMA cycles, while the eight bit processor
in the 64180 performs only eight bit memory access cycles. Sixteen bit DMA
is achieved by hardware shifting of the DMA addresses one bit (effectively
multiplying the address by two and changing the DMA auto–increment from
byte to word) and by manipulating the control strobe. Software adjusts the
addresses provided to the DMA controller when it is programmed for sixteen
bit DMA. This manipulation saves both the added cost of a sixteen bit DMA
controller and the second cycle that an eight bit transfer would require.
Serial Input One of the 64180 UARTs handles serial communication with
the host. Additional modem control lines are provided in the 64180 hardware
control register.
Communicating with the Operator
The synchronous serial port in the 64180 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.
Printing
Hammer Driver Interface
The 64180 programs the dot plucker ASIC and
the FTIC every stroke, 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 64180 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
64180 programs the PFC 8032 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 with a command to move paper immediately. This