Black Box PS035A - Manual (Page 7)

PQ-6 PLUS (RO)
6
2. Introduction
2.1 Application
The PQ-6 PLUS (RO) is a “receive-only” microprocessor-based printer interface for the IBM System/34,
System/36, and System/38 computers. It allows a printer with an RS-232 or Centronics compatible port to
interface with IBM twinaxial cable via a male DB15 and twinax “pigtail” cable. Device address and serial or
parallel output are switch selectable, and the baud rate is selectable in 16 settings from 50 to 19,200 bps.
XON/XOFF and DTR are supported by the PQ-6 PLUS (RO) for buffer control. Data format is 7 bits, space
parity, 1 stop or 8 data bits, no parity, 1 stop bit.
2.2 Description
Data and commands are received from the twinax cable serially (1-MHz clock) by the proprietary front-end
processor of the PQ-6 PLUS (RO). Those commands and data addressed to the PQ-6 PLUS (RO) as
determined by the device address selection switches, are passed to the Z-80A microprocessor for further
processing. The Z-80A CPU converts EBCDIC to ASCII and makes the protocol conversions it needs to change
the high-speed synchronous twinax input into an asynchronous RS-232 ASCII output or Centronics compatible
output. You may bypass the EBCDIC to ASCII controller to the printer using the PQ-6 PLUS (RO) command-
passthrough feature (see Section 4.3).
Input data from the controlling host consists of data and command sequences normally interpreted by an
IBM 5256, 5224, and 5225 printer. In addition to printable characters and carriage-control characters (such as
new line, carriage return, and line feed), the controlling host can send command sequences to control output
format. These commands include page width, page length, characters-per-inch, and horizontal and vertical
carriage-positioning sequences. The PQ-6 PLUS (RO) interprets these command sequences and outputs ASCII
characters to perform the appropriate function. For example, when a form length command is received, the
value is stored internally in the PQ-6 PLUS (RO); when it receives a request for a form feed or for an absolute
move to line one of the next page, the PQ-6 PLUS (RO) will cause the paper in the attached printer to eject a
form of the previously specified form length. Since some commands issued to IBM printers cannot be easily
implemented on RS-232 ASCII printers, these commands are interpreted by the PQ-6 PLUS (RO) and
discarded. For example, a command to set the lines per inch to seventy-two is accepted by the PQ-6 PLUS
(RO), but no corresponding ASCII sequence is output, since the PQ-6 PLUS (RO) cannot know in advance
whether the attached printer can accommodate such a command and how to implement it.
As shipped from the factory, the PQ-6 PLUS (RO) is configured to emulate an IBM 5256 printer. If the PQ-6
PLUS (RO) is to emulate the 5224 or 5225 printer, you need to set the appropriate switch on the printed circuit
board (see Section 4.5).
Serial transmission speed is switch-selectable via printed-circuit-board switches, up to 19,200 bps. Output data
is asynchronous with one start bit, seven data bits, space parity, and one stop bit.
The PQ-6 PLUS (RO) supports both software flow control via XON/XOFF characters and hardware flow
control via the DTR RS-232 input lead. The PQ-6 PLUS (RO) will suspend printing whenever the DTR signal
drops and will resume printing when DTR is asserted. Similarly, when it receives an XOFF character (hex 13),
the PQ-6 PLUS (RO) suspends printing; when it receives an XON (hex 11), it will resume printing. Both
methods are always enabled. No configuration is required.