hpplot - simple tool to send data to an HPGL plotter

This is a quick 'n dirty tool to send an HPGL file to a Hewlett-Packard plotter, with support for various kinds of flow control, and a couple of useful filters to make changes to the HPGL stream that is sent.

Installation

git clone https://github.com/rhalkyard/hpplot
cd hpplot
pip install .

Usage

To plot a file called plot.hpgl to a plotter attached to /dev/ttyUSB0 at 9600 baud, overriding the pen velocity to 15.5 cm/s:

hpplot --baud-rate 9600 --velocity 15.5 /dev/ttyUSB0 plot.hpgl

On Windows, serial port names such as COM1 can be used instead.

Arguments

-b BAUD / --baud-rate BAUD

Set the baud rate used when communicating with the plotter. Default is 9600 baud, the fastest speed supported by the HP 7470A.

-f MODE / --flow-control MODE

Set the flow-control mode used in communication with the plotter. The appropriate escape sequences will be sent to the plotter to configure it for the selected mode.

Valid modes are:

• query (default) - query plotter for available buffer space before sending data

• dsrdtr - hardware flow control using DSR control line

• rtscts - hardware flow control using RTS control line

• xonxoff - software flow control using XON/XOFF protocol

• enqack - software flow control using ENQ/ACK protocol

Note that dsrdtr and rtscts flow control require a suitably-wired RS232 cable, connecting pin 20 (DTR) on the plotter to DSR for dsrdtr, or to CTS for rtscts.

xonxoff flow control requires that the serial adapter's driver supports XON/XOFF flow control. Some USB-serial adapters are buggy when operating in this mode, or simply do not support it!

The query and enqack flow-control modes are implemented entirely within the hpplot tool itself, and should work on any serial interface. In practice, the default query mode should be fine for all uses, I just implemented the others out of the sake of curiosity.

See the HP 7470A Interfacing and Programming Manual for details about the plotter's behavior in each flow control mode.

-B BLOCKSIZE / --block-size BLOCKSIZE

Flow-control block size. This value is interpreted slightly differently based on the flow control mode - see the HP 7470A Interfacing and Programming Manual for details. Default is 80 bytes, the default block size used by the HP 7470A. There shouldn't be much need to change this.

-p / --no-pen-select

Suppress any SP commands in the HPGL stream. This is useful when adapting full-length pens for use in the plotter, as they will cause the mechanism to jam if a pen-change operation is requested.

-v VELOCITY / --velocity VELOCITY

Set the pen velocity, overriding any VS commands in the HPGL stream.

Compatibility

I have only tested hpplot with a 7470A, but it should work with other HP plotters (and clones) that use HPGL and a similar set of configuration escape sequences.

HPGL processing

Note that the -p/--no-pen-select and -v/--velocity options cause hpplot to rewrite commands in the HPGL stream. These options assume that each HPGL command is terminated with ; - a convention that is usually adhered to, but not strictly required by all commands. Additionally, substrings of text printed using the LB command may get mis-identifed as commands to rewrite.

The arguments for the -b/--block-size and -v/--velocity arguments are not checked for range, as their valid ranges differ for different plotter models. Valid block sizes for the 7470A range from 1 to 255 bytes, and pen speeds from 1 to 38.1 cm/s.