SLP440

This is an SLP 440:

It's a label printer that can be operated both by serial and USB. Since the serial interface is simpler than the USB, I chose to use the serial.

Hardware

In order to allow the mbed to communicate via serial, an RS232 level shifter must be made. The mbed can then be connected through the level shifter to a male D-connector, which in turn connects to the printer. The default baud rate of the SLP440 is 115,200. Make sure you wire up the serial port correctly: the red PCB you can see in the picture is printed wrongly, as it is in fact for the other gender of plug. As a result, I initially wired it up incorrectly and could not work out what was wrong.

Notice the sticker on the chip produced with the printer.

The printer sends XON/XOFF signals to tell the mbed whether it'll recieve any more input.

Software

A detailed documentation of the printer can be found on the manufacturers website (or at the bottom of this page). Each command was laboriously turned into a member function of the class SLP440, to allow easy calling. By combining this library with the BitmapFile library, bitmaps stored on the chip can be printed to the printer. Color images are first converted (poorly) to black and white, since the printer is not color.

Sample program

This program loads a bitmap named "mbed.bmp" stored in the flash memory, then prints it out onto a label. This is how the label on my chip was printed.

#include "mbed.h"
#include "SLP440.h"
#include "BitmapFile.h"

Serial pc(USBTX, USBRX);
SLP440 printer(28,27);

LocalFileSystem local("local");

int main()
{
    BitmapFile MyBitmap("/local/mbed.bmp");
    for(int row = MyBitmap.getHeight()-1; row >=0 ; row--)
    {
        char *bitstream = MyBitmap.getRowBitstream(row,false);

        /* these lines used to invert picture */
        int bytes = (MyBitmap.getWidth()+7)/8;
        for(int col=0; col<bytes; col++)
        {
            bitstream[col] = ~bitstream[col];
            if(col+1 == bytes)
            {
                bitstream[col] ^= 0xFF>>(8-(bytes*8-MyBitmap.getWidth()));
            }
        }
        /* end of picture inversion */

        printer.Print(bytes,bitstream);
        delete [] bitstream;
    }
    MyBitmap.close();
    printer.FeedLabel();
}

Here is the image I used on my chip:

API

The library is avaliable from:

• http://mbed.co.uk/projects/cookbook/svn/SLP440

SLP440	A class to use an SLP440 label printer.
Functions
WaitForEmptyBuffer	Waits for the printer to accept data.
SLP440	Creates an instance of the SLP440 class.
Print	Print literal (binary) data
PrintRLE	Print compressed (RLE) data
SetMargin	Set offset (in mm) from left side
RepeatPrint	Repeat last print command
Tab	Tab a number of dots to the right
LineFeed	Feed label one dot
VTab	Feed label a number of dots
FeedLabel	feed to top of next label
SetSpeed	Set printer speed mode
SetDensity	Set printer density
Reset	Reset printer
ReverseFeed	Feed paper backwards a number of dots
Checkpoint	send checkpoint response
GetModelNum	Request printer model number
SetIndent	Set image offset in dots from left side
SetFineMode	Set anti-banding mode on/off
SetXOFFThreshold	Set XOFF threshold
SetXONThreshold	Set XON threshold
EnableDiagnostics	Enable diagnostic mode
SetSerialNo	Set serial number
SetOptions	Change option settings
GetOptions	Request option settings
SetMode	Set printer mode
GetMode	Get printer mode
SetLabelLength	Set the label length in millimeters
CheckBaudRate	Check for correct baud rate

class SLP440

A class to use an SLP440 label printer.

void WaitForEmptyBuffer()

Waits for the printer to accept data.

SLP440( int  tx, int  rx )

Creates an instance of the SLP440 class.