List 1029

By Eddie Cross

 

Issue 25

Jan/Feb 87

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Anyone who purchased the 1029 printer to enable them to debug programs will almost certainly be disappointed in that it does not print anything like the full range of characters that appear on the TV screen. All is not lost, however, as the 1029 is capable of both Bit Image Mode and International Character mode which together can be used to print those 'unprintable' characters.

The accompanying program can be used to print any program that has been LISTed to disk and will show all control characters as well as inverse characters in much the same way as the listings in PAGE 6. The program to be printed must be in LISTed form on disk. Just run the program and follow the prompts. The length of line for the printer is requested, defaulting to the normal screen width of 38 but this can be overtyped. The number of lines per page can also he similarly altered. Enter the filename to be printed without using 'D:' or quotation marks. The program will default to drive 1. When the file has been located, the screen is turned off and printing begins.

Once the number of lines per page has been reached the screen is turned on and the message 'NEW PAGE' appears. You may now adjust the paper or insert another sheet before pressing RETURN to continue.

The listing is offset from the left margin by using a standard tab (',') in line 110 which will allow for hole punching for storage and the page heading and page numbering is printed in double width.

For those who would like some more information on how the program works I will provide some brief notes.

FORMING CHARACTERS

Firstly it is important to understand how characters are formed in Bit Image Mode. The printed character is made up of a matrix of 7 dots high by 5 dots wide (compared with a screen image of 8 pixels high by 8 wide). In Bit Image Mode it is possible to address single dots column by column. Standard binary is used but as the matrix is only 7 dots high only a maximum of 127 can be used in each column. This would give a full vertical line.

Each of the 5 columns is constructed as follows:

 Top Dot

 ... 64

 

 ... 32

 

 ... 16

 

 ... 8

 

 ... 4

 

 ... 2

 Bottom

 ... 1

To construct a line of dots in the first column of, say, the top, second to bottom and bottom rows, simply add up the values for each row and write this as a DATA statement:

10 DATA 69

Now repeat for all five columns to build up the necessary shape of the character:

10 DATA 69,111,65,13,127

An additional point to note is that although the 1029 uses five columns for a character it normally also prints a sixth blank column to separate the characters and this rule must be obeyed in order to use the Bit Image Mode to print alternative characters. So, a 6th line of dots (in this case no dots) must be added so the data must end in 0:

10 DATA 69,111,65,13,127,0

BIT IMAGE MODE

To put the 1029 in Bit Image Mode it is necessary to send the code ESC ESC A to the printer. This must be followed by the Most Significant Bit (MSB) and the Least Significant Bit (LSB) denoting the number of rows of data to be sent to the printer. In this case, since we have only 6 rows of data the MSB= 0 and LSB=6.

The routine for sending the Bit Image data is in lines 360 to 420 of the program:

Line 360 sends the instruction to Set Bit Image Mode, MSB and LSB.

Line 370 selects the DATA line that contains the matrix to be printed. It is 1000 plus the ATASCII code for a particular character. For example, the ATASCII code for Inverse CONTROL B is 130 so line 1130 contains that data.

Lines 380 to 410 read the DATA statement and prints the individual columns of selected dots. Line 420 returns to the main program to find the next character to be printed.

INTERNATIONAL CHARACTERS

So much for 'non-standard' characters but there are in fact several characters that the 1029 can print without using the Bit image Mode and constructing DATA statements. These are included in the 'International Character Set' and include such characters as 'clear screen' and 'cursor arrows'.

These can be printed simply by putting the 1029 into International mode by sending the codes ESC CONTROL-W to turn on the mode and ESC CONTROL-X to turn it off. Line 330 of the program does this.

The heart of the program lies between lines 120 and 220. Each character to be printed is read from the disk (GET #1,A) and the ATASCII value is checked. If the character is not one which can be printed normally, the program goes to the subroutine for either Bit Image Mode or International Mode as appropriate. If the character is standard the program continues to line 200 where it is printed as normal.

One slight drawback is that some characters, being normally 8 bits wide are difficult to fit into a 5 dot matrix so the sixth dot has to be used and the spacing is lost. The results however are still quite legible.

I hope that 1029 owners will find new uses for their printer with the information in this article and program. It should be quite simple, for instance to print the elusive sign with a little thought. Remember it is ATASCII code 8 or CONTROL-H in International mode.

AtariLister - requires Java

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