As I have said before, I have a lot of software and items that I have picked up in job lots, and I still have to sort out and install to see what I can do with it. Having EUG published bi-monthly gives me an incentive to do this - hence the above title.
When writing items for EUG, I am conscious that:
- a lot of members know far more about computing than I do - especially programming;
- some members will have the software/equipment that I write about, and
- I hope what I do write will be interesting and useful to readers.
Having got that off my chest, the following few notes are about the above two ROMs that I am currently experimenting with to see what can be produced. One thing that I have just found a few mements ago is that, being in Mode 7 then trying to go to Click crashes the computer - one has to type, say, MODE 6 (RETURN), then *CLI (RETURN).
Another thing I have just found is that if the SIMULATOR ROM is left live whilst in View and there is a crash, then the computer goes to Mode 7 when brought back on line, though the View program is not lost. Normally I would have the ROM killed by Click whilst using View.
The computer I am currently using is not fitted with the Mk.2 unit, which has a special board inside the Electron, though I do have another Electron so fitted. I have the full 16 pages with this Electron and can call up both ROMs - the Mk.2 in page 13 and the SIMULATOR in page 1. To get to Mode 7, both ROMs have the came command (*MODE7ON/BREAK) and therefore, the Mk.2 should take precedence.
Just to see what would happen on the command *MODE7ON/BREAK, I brought both ROMs live into the system and issued the command. The computer does not crash but goes straight to the MODE7 with the MODE 7 SIMULATOR ROM. However, I normally would have page 13 killed via Click until I needed a specific ROM in the ROM128.
According to the manuals, both ROMs are better used with the Master RAM Board, and both ROMs will work with the BBC ROM WORDWISE+ word processor.
What I am experimenting with at present is seeing what I do with the Teletext control codes. Here one also needs the BBC USER GUIDE for Jafa assumes anyone using Mode 7 on the Electron will be familiar with the BBC computer! Not necessarily so! I do find using the codes is a bit tedious, but patience is a virtue. One good thing is that there are tables in the back of the User Guide that give codes for the Teletext Displayed Graphic Characters, and the Teletext Displayed Alphanumeric Characters. However, codes can be calculated as follows:
_______________
| | |
(1) | 1 | 2 | (2)
|_______|_______|
| | |
(3) | 4 | 8 | (4)
|_______|_______|
| | |
(5) | 16 | 64 | (6)
|_______|_______|
The graphic shapes are calculated from a combination of a selection of squares from a 2 by 3 grid and each square has a value as shown above. I have numbered the squares from (1) to (6) for ease of description. Say that one wanted a shape made up of squares (2), (4) and (5). The code shown in the table for this is 186. It is calculated by adding up the value of the squares selected and then adding 32 and 128, thus:
| 2+8+16+32+128 = 186 |
Having selected this shape we can print it out anywhere on the screen and in a selected colour, say, red. The code for red in graphics is 145 so:
PRINTTAB(X,Y);CHR$(145);CHR$(154);CHR$(186)
will do the trick. Code 154 is necessary for separated graphics The background colour can also be changed by a slightly more elaborate procedure. You can begin to see how the programming becomes a little tedious! It is easier, I think, to use the VDU format, hence two lines of a program might be:
PRINTTAB(X,Y);
VDU145,154,186
This will print the red shape at (X,Y).
The Mode 7 screen is X: 0-39 and y: 0-24. (0,0) is the top left-hand corner. It follows that the highest code is for whole block at 255, so 1+2+4+8+16+64+32+128 = 255, and the lowest 161 for just square (1). Code 160 is no square selection at all though it could be printed by suitable colour selection.
A lot of the codes below 160 do nothing at all, but others operate the printer, produce double-height letters, produce colours (steady or flashing), produce beeps, move the cursor around (useful in making up pictures using the codes shapes) and other functions. So one can begin to see that pictures like ITV's Bamber Boozler can easily be produced - even if, as I have said, the programming is a bit tedious - at least first time round. I can see that with time one could build up a series of connected shapes to use to make pictures and keep them on disk to bring into programs as and when required.
It is interesting to note that colour selection requires differing codes for the same colour depending whether alphanumeric or graphics is operable.
Another point is that there are no MOVE or DRAW commands in Mode 7. Separate procedures have to be written to produce lines or curves.
- MODE7ON and MODE7OFF.
- MODE7. Toggles between the two.
- EFN. Interpret function keys as Electron function keys.
- BFN. Interpret function keys as BBC micro SHIFT/CTRL function keys. This is the default when the ROMs are active.
- MCOMM. If one has the required additional equipment Prestel can be dialed up.
- TELETEXT. Again if the required equipment is available, TELETEXT can be received. (I have the equipment for this for the BBC Micro.)
The following commands are appropriate to the MODE 7 SIMULATOR ROM only:
- MRAP. Select rapid updating mode._The_default with WORDWISE or the Master RAM Board active.
- MNORM. Select normal updating mode. The default when neither WORDWISE or the Master RAM Board are active.
The following commands are appropriateto the Mk.2 ROM only:
- GREEN. Select green screen monitor mode.
- MED. This is demonstration screen editor and_edited_screens can be SAVEd if required.
Additionally, when both ROM's are active they respond to:-
- *HELP_BARS._Gives colour bars on the monitor to facilitate colour adjustment and contrast.
- *TV n. If n=1,_the display_is moved up. If n=254, the display is moved down. But unlike the BBC, lines are lost with the Electron.
Here endeth the lesson by the Elder(ly novice)!
Tony Boarer, EUG #29