Start-Stop Printer Attachment; Timing And Control Logic; Start-Stop Adapter Example Operation - IBM 5280 Technical Newsletter

Start-Stop Printer Attachment
The start-stop printer attachment consists of the start-stop
printer adapter and the start-stop printer attachment MPU.
The start-stop printer adapter controls the transfer of data
and commands to the printer as instructed by the start-stop
printer attachment MPU. Each printer is attached by a four-
wire, twisted pair, start-stop cable to a port of the start-stop
printer adapter.
The start-stop printer adapter sends commands and data to
the printer and receives status information from the printer
in an 11-bit start-stop frame. The 11-bit start-stop frame is
described later in this section (see
11-Bit Frame Concept).
Refer to logic diagram LD18 in the System Logic Manual
while you read the following description.
The components of the start-stop printer adapter are as
follows:
• Driver/receivers (one for each port)
• Timing and control logic
• Port control logic
• Serdes (serializer/deserializer-asynchronous receive/
transmit logic)
Driver /Receivers
The driver/receivers provide the interface between the start-
stop printer adapter and the start-stop cable. One driver/
receiver circuit is provided for each port. The receiver
accepts incoming data from the receive pair of the four-wire
start-stop cable and the driver transmits data on the transmit
pair of the cable in a full duplex mode. .
Timing and Control Logic
The timing and control logic provides the clocks for
operation of the serdes. The control logic provides gating
and control lines which operate as directed by commands
issued by the start-stop printer attachment MPU.
Port Control Logic
The port control logic uses control lines from the control
logic to select either internal wrap mode or gating to the
start-stop cable.
Page of SY31-0600-1
As updated April 15, 1981
By
TN
L
SN20-9588
Serdes
The serdes accepts data from the 100 register and converts
the data from parallel to serial. The serdes also formats
the data into an 11-bit frame by adding the proper start and
stop bits to the data for transmission to the printer. The
serdes converts the serial data received from the printe',. to
parallel data and signals the start-stop printer attachment
MPU that data is available from the printer.
START-STOP ADAPTER EXAMPLE OPERATION
The following example shows how data is sent from main
storage to an attached printer:
1.
2.
3.
4.
5.
When the main MPU reads a printer write instruction,
it places the instruction in the printer lOB and turns
on the attention line to the start-stop printer attach-
ment MPU.
The start-stop printer attachment MPU senses the
attention line and reads the instruction in the lOB (see
Main Storage Accessing in this section for an example
of how an MPU accesses main storage to read or write
data).
The start-stop printer attachment MPU receives the
data from the main MPU and transfers the data to the
printer storage area in main stor,age. The start-stop
printer attachment then performs calculations to deter-
mine how much data is to be sent to the printer in
each block,.
The start-stop printer attachment MPU issues a read
status command to the start-stop printer adapter. The
start-stop printer adapter loads the serdes status byte
into the 100 register. The start-stop printer attach-
ment MPU then reads and evaluates the contents of
the 100 register. If no errors or "break received"
indication is present, the start-stop printer attachment
MPU prepares to send data to the printer by issuing
write control information commands.
A byte of data to be transmitted to the printer is
loaded into the 100 register. A write data command
is then issued inthe EAR register to the start-stop
printer adapter.
Printer Attachment 274.3