Advanced Programming

Here we are again, in the Machine Code Corner. This month, I am going to show you some ROM routines that use the TS2040 printer! But first, an apology.

Last month, I gave you two routines that scrolled part of the screen left and right. For one reason or another, the BASIC loader did not get printed. For those who looked all over the newsletter for it, please forgive me. You will find it at the end of this month’s column, along with a reprint of the HEX codes and mnemonics.

Now some of you, I am sure, know how to print things to the printer from machine code already. For those of you who do not, this month’s discussion should help you along.

First, the PRINTER BUFFER. Located at 23296 decimal, 5B00 hex, it contains information to be dumped to the printer itself. The buffer is only 256 bytes long (FF hex), so the computer can send only so much at one time.

The buffer is set up just like the display file (oh no!), only it is one line of data, 32 bytes wide, and 8 bytes deep, exactly like one line in the display file. This allows you to send bits of information to the printer, instead of just character codes, like other printers.

Now we get to the good stuff. The printer dump routine itself is not that long, if you don’t count the subroutines that it uses. It is located at 2595 decimal, or 0A23 hex. This routine simply takes what is in the printer buffer and sends it to the printer. Then it clears the buffer and returns to where it came from. For those of you who go through the function dispatcher for the printer routines, you no longer need to punish youself with such travesty! You can go straight to the source.

The COPY command from BASIC is just as easily done in machine code as it is to type COPY from the keyboard. The routine to do it is located at 2562 decimal, 0A02 hex. It sets up a loop (for the 22 lines of the screen to be copied), loads the printer buffer with the first 8 “scan” lines (when I say “scan” lines in this column, I mean the 8 horizontal bytes used to form a character on the screen) of the display file, and calls the printer dump routine. Then it counts down the loop, loading the buffer with the next line of data from the display file, dumping it, and so on and so forth until all 22 lines are copied. But what about the bottom two lines of the screen? There are a lot of programs that use those lines and how in the world can I get them to the printer? Read on, my friend…

There is a way to print all 24 lines of the screen to the printer, but it requires just a teensy bit of preparation to do so. Also, you need to call a different address in the ROM. Here is what you need to do. Load your hex loader or assembler, or if you don’t have one, get out the BASIC loader below and type the routine in. After doing so, PLEASE (!!!) save it to tape. Here is the HEX codes with mnemonics, with the BASIC loader following:

24 Line Screen Dump

(This routine can be located anywhere in memory.)

FF46  F3          DI            TAKE OUT INTERRUPTS
FF47  06 C0       LD B,C0H      LET B=192
FF49  CD 05 0A    CALL 0A05H    RANDOMIZE USR 2565
FF4C  C9          RET           BACK TO CALLER

10 FOR N=65350 TO 65356: READ X: POKE N,X: NEXT N
15 DATA 243,6,192,205,5,10,201

There you have it. All 24 lines to the printer. You can change the 192 in the BASIC loader or the C0 in the hex listing, so that you could copy only 8 lines of the screen… Just change it to 64 decimal in the BASIC loader and in the hex listing, to 40 hex. Very simple!

If you want to print more or less than that, all you must do is change the B register to however many “scan” lines you want printed. Keep in mind that it counts from the top of the screen, so you can’t copy the middle of the screen, unless you use yet another routine…

The next routine I am going to give you can be used to copy nearly any part of the screen, 32 columns across (I haven’t worked out a way to print only 16 columns yet).

You must first find out the address of the first byte to copy (it can be anywhere in the display file), and then find out how many “scan” lines you want to print. Then you call the ROM routine! Here it is:

Part-Copy Routine

(This routine can be located anywhere in memory.)

21 NN NN    LD HL,NNNN    HL=START OF COPY\n06 NN       LD B,NN       B=# OF SCAN LINES
F3          DI            TAKE OUT INTERRUPTS
CD 08 0A    CALL 0A08H    RANDOMIZE USR 2568
C9          RET           BACK TO CALLER

10 FOR N=65350 TO 65359: READ X: POKE N,X: NEXT N
15 DATA 33,NN,NN,6,NN,243,205,8,10,201

NOTE: “NN” means you put in your own numbers or ones off of the following table! Here are some key spots on the screen:

Hex	Decimal		Comment
4000	16384	(0,64)	AT 0,0
4020	16416	(32,64)	AT 1,0
4040	16448	(64,64)	AT 2,0
4060	16480	(96,64)	AT 3,0
4080	16512	(128,64)	AT 4,0
40A0	16544	(160,64)	AT 5,0
40C0	16576	(192,64)1	AT 6,0
40E0	16608	(224,64)	AT 7,0
4800	18432	(0,72)	AT 8,0
4820	18464	(32,72)	AT 9,0
4840	18496	(64,72)	AT 10,0
4860	18528	(96,72)	AT 11,0
4880	18560	(128,72)	AT 12,0
48A0	18592	(160,72)	AT 13,0
48C0	18624	(192,72)	AT 14,0
48E0	18656	(224,72)	AT 15,0
5000	20480	(0,80)	AT 16,0
5020	20512	(32,80)	AT 17,0
5040	20544	(64,80)	AT 18,0
5060	20576	(96,80)	AT 19,0
5080	20608	(128,80)	AT 20,0
50A0	20640	(160,80)	AT 21,0
50C0	20672	(192,80)	AT 22,0 — INPUT AREA
50E0	20704	(224,80)	AT 23,0 — INPUT AREA

Well, there you have it. All you have to do is copy the numbers in parentheses () off of the table and into the BASIC loader. Then set up the B register with the number of scan lines, and call the routine!

Now, for that BASIC loader for SCREEN SCROLL:

1 REM SCREEN SCROLL- USR 65280 FOR LEFT, USR 65298 FOR RIGHT.
5 CLEAR 65279
10 FOR N=65280 TO 65315: READ X: POKE N,X: NEXT N
15 DATA 33,255,71,14,32,167,203,22,43,13,32,250,62,64,188,32,242,201
20 DATA 33,0,64,14,32,167,203,30,35,13,32,250,62,72,188,32,242,201

Here is the HEX dump:

TOP THIRD TO THE LEFT

FF00  21 FF 47    LD HL,47FFH   HL=18431
FF03  0E 20       LD C,20H      C=32
FF05  A7          AND A         CLEAR CARRY
FF06  CB 16       RL (HL)       SEE JULY NEWSLETTER
FF08  2B          DEC HL        HL=HL-1
FF09  0D          DEC C         C=C-1
FF0A  20 FA       JR NZ,FF06H   GOTO FF06 IF C<>0
FF0C  3E 40       LD A,40H      A=64
FF0E  BC          CP H          IF A=H THEN SET Z FLAG
FF0F  20 F2       JR NZ,FF03H   GOTO FF03 IF H<>A
FF11  C9          RET           BACK TO CALLER

TOP THIRD TO THE RIGHT

FF12  21 00 40    LD HL,4000H   HL=16384
FF15  0E 20       LD C,20H      C=32
FF17  A7          AND A         RESET CARRY FLAG
FF18  CB 1E       RR (HL)       SEE JULY NEWSLETTER
FF1A  23          INC HL        HL=HL+1
FF1B  0D          DEC C         C=C-1
FF1C  20 FA       JR NZ,FF18H   GOTO FF18 IF C<>0
FF1E  3E 48       LD A,48H      A=72
FF20  BC          CP H          IF A=H THEN SET Z FLAG
FF21  20 F2       JR NZ,FF15H   GOTO FF15 IF Z FLAG NOT SET
FF23  C9          RET           BACK TO CALLER