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Transmitted Data
(TD)
and Received Data
(RD)
lines are connected to the
universal synchronous asynchronous receiver/transmitter
(USART)
through a
transmitter/receiver
(T/R).
The Data Terminal Ready
(DTR),
Request to Send
(RTS),
and Clear
to
Send
(CTS)
control lines are provided for these data lines
and are also connected to USART through the T/R.
The
USART
transmit/receive request line
(IRQ)
is connected
to
the interface
microprocessor
(MPU)
via
&bit
bus lines and address lines. The bus and
address lines
are
also connected to the interface buffer and internal bus MPU.
The interface MPU operation is controlled by microprograms stored in the ROM.
Microprogram execution is described below.
-
Receiving data
When one-word data is generated in the
USART
from the serially sent data, the
USART
issues a receive request interrupt to the interface MPU. The interface
MPU reads the data, decodes it, and checks whether it is a Status Request
command. If not,
the interface MPU stacks the data in the interface buffer.
If so, it responds with the printer status.
-
Transmitting data
When data transmission is necessary (for the printer status
reponse,
XON/XOFF
transmission, or local loopback test), the interface MPU
USART
data and
writes data in the USART every time the LJSART issues a transmit request
interrupt.
-
Commands to the internal bus
MPU
When writing data into the interface buffer begins,
the!
interface MPU detects
a control code or control sequence written in the interface buffer and
decodes it,
than issues a command to the internal bus
MPU.
Whether the command sent from the internal bus MFU terminates or not, if a
mechanical error or operator intervention request (indicated by the
Intervention Required signal) occurs, it is reported to the interface
MPU.
If the command termibates normally,
the interface
MPIJ
issues the next
command.
If printer operation is stopped due to a mechanical error or an operator
intevention
request (the internal bus MPU cannot operate in this state), the
interface MPU stops issuing the next command to the internal
MPU
and stops
reading data in the interface buffer until the mechanical error is corrected
or the operator intervention request ends.
The amount of data transmitted from the host can be reduced by the Repeat
Character command or the Move Horizontal Position command or by the Horizontal
Tabulation
(HT)
code using horizontal tab stop data downloaded by the Load
Horizontal Tab Stop Data command.
A line feed pitch of
6/8
lpi can be selected by the Select Vertical Pitch
command.
A half-line feed pitch of 12 lpi can also be selected by using the
Half Line Feed command.
Responding to the Status Request command from the host, the printer reports its
status
(startus
response).
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