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+P5
This website contains an archive of files for the Acorn Electron, BBC Micro, Acorn Archimedes, Commodore 16 and Commodore 64 computers, which Dominic Ford has rescued from his private collection of floppy disks and cassettes.
Some of these files were originally commercial releases in the 1980s and 1990s, but they are now widely available online. I assume that copyright over them is no longer being asserted. If you own the copyright and would like files to be removed, please contact me.
| Tape/disk: | Home » Personal collection » Acorn ADFS disks » Electron_User_Group » EUG_38.ADF |
| Filename: | +P5 |
| Read OK: | ✔ |
| File size: | 1341 bytes |
| Load address: | 2B204556 |
| Exec address: | D3550 |
Duplicates
There is 1 duplicate copy of this file in the archive:
- Personal collection » Acorn ADFS disks » Electron_User_Group » EUG_38.ADF » +P5
- Personal collection » Acorn hard disk » zipped_disks » elk03 » eug38/+P5
File contents
Now that you can locate a the memory occupied by a character in screen memory, you need to know how the bytes within this block are laid out, so that you can have pixel by pixel control over your monitor screen. This is also required if you are to be able to calculate the amount of memory taken up by each character's definition in a particular mode. The graphics modes can be divided into three categories: monochrome modes (ie. two colours), four colour modes, and sixteen colour modes. All of the Elk's modes fall into these three groupings. Which of these colours each pixel of the screen is depends upon the status of a number of binary bits. These have two states, 0 or 1. Now, in a monochrome mode, one bit is sufficient to define the colour of one pixel (bits have two states, 0 or 1, and the pixels have two states, colour 0 or colour 1). In a four colour mode, on the other hand, one bit will not be sufficient, as four different states are required. Two bits will be enough to store the colour of one pixel, however: Bit 1 state Bit 2 state Colour 0 0 0 0 1 1 1 0 2 1 1 3 Those familiar with binary will spot the pattern straight away - simply convert the binary value of the two bits into decimal, and you have the logical colour number. A very similar pattern applies to MODE 2 - the Elk's 16 colour mode. Each pixel requires 4 bits to store its colour (2^4=16). Once again, the colour of the pixel is the logical colour whose number is given when four bits are put together to form a binary value: Bit 1 state Bit 2 state Bit 3 state Bit 4 state Colour Default 0 0 0 0 0 BLK 1 0 0 0 1 RED 0 1 0 0 2 GRN 1 1 0 0 3 YEL 0 0 1 0 4 BLE 1 0 1 0 5 MGN 0 1 1 0 6 CYN 1 1 1 0 7 WHT 0 0 0 1 8 BLK/WHT 1 0 0 1 9 RED/CYN 0 1 0 1 10 GRN/MGN 1 1 0 1 11 YEL/BLE 0 0 1 1 12 BLE/YEL 1 0 1 1 13 MGN/GRN 0 1 1 1 14 CYN/RED 1 1 1 1 15 WHT/BLK [Default: Default setting of this logical colour when MODE 2 is first entered] So... the Electron has modes where the definition of the colour of a certain pixel can take 1, 2 or 4 bits. As each byte of the electron's memory consists of 8 seperate bits, this means that in monochrome modes we can fit 8 pixels into each byte (8/1=8). In four colour modes (where each pixel requires two bits) we can fit 4 pixels into each byte (8/2=4). Finally in MODE 2 (the sixteen colour mode where each pixel requires 4 bits) we can fit two pixels into each byte. Let's now look at how each is laid out in more depth: MONOCHROME MODES: These are laid out in the simplest way, as eight pixels fit into each byte. The character, remember, consists of an 8-by-8 square of pixels. The data is stored in the same way as user defined characters are defined using VDU 23. The first byte of the definition defines the top row of eight pixels; the second defines the second row down, etc. Thus the entire character can be defined in eight bytes, and this is the number of bytes of the Elk's memory which is used by each character's definition. Note - the most significant bit of each byte defines the left-most pixel of the row, and the least significant bit defines the right-most pixel (just as with VDU 23 definitions). FOUR COLOUR MODES: This time each byte can only hold four pixels. Once again, each byte holds a number of pixels which are in a horizontal line. This time, as before, the first eight bytes run down in a vertical line. The difference this time, though, is that not all of the pixels in the character are being defined by the one sweep, and instead only the left-most four pixels can be defined. The right-most four pixels are defined in a second downward vertical sweep. Thus the total memory allocation for the definition of each character is sixteen bytes. The layout of these is shown more clearly by the diagram below. This shows the eight-by-eight block of pixels in a character, and each has the offset of the memory location where this pixel is stored from the start of the character definition. Offsets are given in hexadecimal:
00000000 0d 4e 6f 77 20 74 68 61 74 20 79 6f 75 20 63 61 |.Now that you ca| 00000010 6e 20 6c 6f 63 61 74 65 20 61 20 74 68 65 20 6d |n locate a the m| 00000020 65 6d 6f 72 79 20 6f 63 63 75 70 69 65 64 20 62 |emory occupied b| 00000030 79 20 61 20 63 68 61 72 61 63 74 65 72 20 69 6e |y a character in| 00000040 20 73 63 72 65 65 6e 0d 6d 65 6d 6f 72 79 2c 20 | screen.memory, | 00000050 79 6f 75 20 6e 65 65 64 20 74 6f 20 6b 6e 6f 77 |you need to know| 00000060 20 68 6f 77 20 74 68 65 20 62 79 74 65 73 20 77 | how the bytes w| 00000070 69 74 68 69 6e 20 74 68 69 73 20 62 6c 6f 63 6b |ithin this block| 00000080 20 61 72 65 20 6c 61 69 64 20 6f 75 74 2c 20 73 | are laid out, s| 00000090 6f 0d 74 68 61 74 20 79 6f 75 20 63 61 6e 20 68 |o.that you can h| 000000a0 61 76 65 20 70 69 78 65 6c 20 62 79 20 70 69 78 |ave pixel by pix| 000000b0 65 6c 20 63 6f 6e 74 72 6f 6c 20 6f 76 65 72 20 |el control over | 000000c0 79 6f 75 72 20 6d 6f 6e 69 74 6f 72 20 73 63 72 |your monitor scr| 000000d0 65 65 6e 2e 20 54 68 69 73 20 69 73 0d 61 6c 73 |een. This is.als| 000000e0 6f 20 72 65 71 75 69 72 65 64 20 69 66 20 79 6f |o required if yo| 000000f0 75 20 61 72 65 20 74 6f 20 62 65 20 61 62 6c 65 |u are to be able| 00000100 20 74 6f 20 63 61 6c 63 75 6c 61 74 65 20 74 68 | to calculate th| 00000110 65 20 61 6d 6f 75 6e 74 20 6f 66 20 6d 65 6d 6f |e amount of memo| 00000120 72 79 0d 74 61 6b 65 6e 20 75 70 20 62 79 20 65 |ry.taken up by e| 00000130 61 63 68 20 63 68 61 72 61 63 74 65 72 27 73 20 |ach character's | 00000140 64 65 66 69 6e 69 74 69 6f 6e 20 69 6e 20 61 20 |definition in a | 00000150 70 61 72 74 69 63 75 6c 61 72 20 6d 6f 64 65 2e |particular mode.| 00000160 0d 0d 54 68 65 20 67 72 61 70 68 69 63 73 20 6d |..The graphics m| 00000170 6f 64 65 73 20 63 61 6e 20 62 65 20 64 69 76 69 |odes can be divi| 00000180 64 65 64 20 69 6e 74 6f 20 74 68 72 65 65 20 63 |ded into three c| 00000190 61 74 65 67 6f 72 69 65 73 3a 20 6d 6f 6e 6f 63 |ategories: monoc| 000001a0 68 72 6f 6d 65 20 6d 6f 64 65 73 0d 28 69 65 2e |hrome modes.(ie.| 000001b0 20 74 77 6f 20 63 6f 6c 6f 75 72 73 29 2c 20 66 | two colours), f| 000001c0 6f 75 72 20 63 6f 6c 6f 75 72 20 6d 6f 64 65 73 |our colour modes| 000001d0 2c 20 61 6e 64 20 73 69 78 74 65 65 6e 20 63 6f |, and sixteen co| 000001e0 6c 6f 75 72 20 6d 6f 64 65 73 2e 20 41 6c 6c 20 |lour modes. All | 000001f0 6f 66 20 74 68 65 0d 45 6c 6b 27 73 20 6d 6f 64 |of the.Elk's mod| 00000200 65 73 20 66 61 6c 6c 20 69 6e 74 6f 20 74 68 65 |es fall into the| 00000210 73 65 20 74 68 72 65 65 20 67 72 6f 75 70 69 6e |se three groupin| 00000220 67 73 2e 20 57 68 69 63 68 20 6f 66 20 74 68 65 |gs. Which of the| 00000230 73 65 20 63 6f 6c 6f 75 72 73 20 65 61 63 68 0d |se colours each.| 00000240 70 69 78 65 6c 20 6f 66 20 74 68 65 20 73 63 72 |pixel of the scr| 00000250 65 65 6e 20 69 73 20 64 65 70 65 6e 64 73 20 75 |een is depends u| 00000260 70 6f 6e 20 74 68 65 20 73 74 61 74 75 73 20 6f |pon the status o| 00000270 66 20 61 20 6e 75 6d 62 65 72 20 6f 66 20 62 69 |f a number of bi| 00000280 6e 61 72 79 20 62 69 74 73 2e 0d 54 68 65 73 65 |nary bits..These| 00000290 20 68 61 76 65 20 74 77 6f 20 73 74 61 74 65 73 | have two states| 000002a0 2c 20 30 20 6f 72 20 31 2e 20 4e 6f 77 2c 20 69 |, 0 or 1. Now, i| 000002b0 6e 20 61 20 6d 6f 6e 6f 63 68 72 6f 6d 65 20 6d |n a monochrome m| 000002c0 6f 64 65 2c 20 6f 6e 65 20 62 69 74 20 69 73 0d |ode, one bit is.| 000002d0 73 75 66 66 69 63 69 65 6e 74 20 74 6f 20 64 65 |sufficient to de| 000002e0 66 69 6e 65 20 74 68 65 20 63 6f 6c 6f 75 72 20 |fine the colour | 000002f0 6f 66 20 6f 6e 65 20 70 69 78 65 6c 20 28 62 69 |of one pixel (bi| 00000300 74 73 20 68 61 76 65 20 74 77 6f 20 73 74 61 74 |ts have two stat| 00000310 65 73 2c 20 30 20 6f 72 20 31 2c 0d 61 6e 64 20 |es, 0 or 1,.and | 00000320 74 68 65 20 70 69 78 65 6c 73 20 68 61 76 65 20 |the pixels have | 00000330 74 77 6f 20 73 74 61 74 65 73 2c 20 63 6f 6c 6f |two states, colo| 00000340 75 72 20 30 20 6f 72 20 63 6f 6c 6f 75 72 20 31 |ur 0 or colour 1| 00000350 29 2e 20 49 6e 20 61 20 66 6f 75 72 20 63 6f 6c |). In a four col| 00000360 6f 75 72 20 6d 6f 64 65 2c 0d 6f 6e 20 74 68 65 |our mode,.on the| 00000370 20 6f 74 68 65 72 20 68 61 6e 64 2c 20 6f 6e 65 | other hand, one| 00000380 20 62 69 74 20 77 69 6c 6c 20 6e 6f 74 20 62 65 | bit will not be| 00000390 20 73 75 66 66 69 63 69 65 6e 74 2c 20 61 73 20 | sufficient, as | 000003a0 66 6f 75 72 20 64 69 66 66 65 72 65 6e 74 20 73 |four different s| 000003b0 74 61 74 65 73 0d 61 72 65 20 72 65 71 75 69 72 |tates.are requir| 000003c0 65 64 2e 20 54 77 6f 20 62 69 74 73 20 77 69 6c |ed. Two bits wil| 000003d0 6c 20 62 65 20 65 6e 6f 75 67 68 20 74 6f 20 73 |l be enough to s| 000003e0 74 6f 72 65 20 74 68 65 20 63 6f 6c 6f 75 72 20 |tore the colour | 000003f0 6f 66 20 6f 6e 65 20 70 69 78 65 6c 2c 0d 68 6f |of one pixel,.ho| 00000400 77 65 76 65 72 3a 0d 0d 42 69 74 20 31 20 73 74 |wever:..Bit 1 st| 00000410 61 74 65 20 20 20 20 20 42 69 74 20 32 20 73 74 |ate Bit 2 st| 00000420 61 74 65 20 20 20 20 20 43 6f 6c 6f 75 72 0d 20 |ate Colour. | 00000430 20 30 20 20 20 20 20 20 20 20 20 20 20 20 20 20 | 0 | * 00000450 20 30 0d 20 20 30 20 20 20 20 20 20 20 20 20 20 | 0. 0 | 00000460 20 20 20 20 20 31 20 20 20 20 20 20 20 20 20 20 | 1 | 00000470 20 20 20 20 20 31 0d 20 20 31 20 20 20 20 20 20 | 1. 1 | 00000480 20 20 20 20 20 20 20 20 20 30 20 20 20 20 20 20 | 0 | 00000490 20 20 20 20 20 20 20 20 20 32 0d 20 20 31 20 20 | 2. 1 | 000004a0 20 20 20 20 20 20 20 20 20 20 20 20 20 31 20 20 | 1 | 000004b0 20 20 20 20 20 20 20 20 20 20 20 20 20 33 0d 0d | 3..| 000004c0 54 68 6f 73 65 20 66 61 6d 69 6c 69 61 72 20 77 |Those familiar w| 000004d0 69 74 68 20 62 69 6e 61 72 79 20 77 69 6c 6c 20 |ith binary will | 000004e0 73 70 6f 74 20 74 68 65 20 70 61 74 74 65 72 6e |spot the pattern| 000004f0 20 73 74 72 61 69 67 68 74 20 61 77 61 79 20 2d | straight away -| 00000500 20 73 69 6d 70 6c 79 0d 63 6f 6e 76 65 72 74 20 | simply.convert | 00000510 74 68 65 20 62 69 6e 61 72 79 20 76 61 6c 75 65 |the binary value| 00000520 20 6f 66 20 74 68 65 20 74 77 6f 20 62 69 74 73 | of the two bits| 00000530 20 69 6e 74 6f 20 64 65 63 69 6d 61 6c 2c 20 61 | into decimal, a| 00000540 6e 64 20 79 6f 75 20 68 61 76 65 20 74 68 65 0d |nd you have the.| 00000550 6c 6f 67 69 63 61 6c 20 63 6f 6c 6f 75 72 20 6e |logical colour n| 00000560 75 6d 62 65 72 2e 20 41 20 76 65 72 79 20 73 69 |umber. A very si| 00000570 6d 69 6c 61 72 20 70 61 74 74 65 72 6e 20 61 70 |milar pattern ap| 00000580 70 6c 69 65 73 20 74 6f 20 4d 4f 44 45 20 32 20 |plies to MODE 2 | 00000590 2d 20 74 68 65 20 45 6c 6b 27 73 0d 31 36 20 63 |- the Elk's.16 c| 000005a0 6f 6c 6f 75 72 20 6d 6f 64 65 2e 20 45 61 63 68 |olour mode. Each| 000005b0 20 70 69 78 65 6c 20 72 65 71 75 69 72 65 73 20 | pixel requires | 000005c0 34 20 62 69 74 73 20 74 6f 20 73 74 6f 72 65 20 |4 bits to store | 000005d0 69 74 73 20 63 6f 6c 6f 75 72 20 28 32 5e 34 3d |its colour (2^4=| 000005e0 31 36 29 2e 0d 4f 6e 63 65 20 61 67 61 69 6e 2c |16)..Once again,| 000005f0 20 74 68 65 20 63 6f 6c 6f 75 72 20 6f 66 20 74 | the colour of t| 00000600 68 65 20 70 69 78 65 6c 20 69 73 20 74 68 65 20 |he pixel is the | 00000610 6c 6f 67 69 63 61 6c 20 63 6f 6c 6f 75 72 20 77 |logical colour w| 00000620 68 6f 73 65 20 6e 75 6d 62 65 72 20 69 73 0d 67 |hose number is.g| 00000630 69 76 65 6e 20 77 68 65 6e 20 66 6f 75 72 20 62 |iven when four b| 00000640 69 74 73 20 61 72 65 20 70 75 74 20 74 6f 67 65 |its are put toge| 00000650 74 68 65 72 20 74 6f 20 66 6f 72 6d 20 61 20 62 |ther to form a b| 00000660 69 6e 61 72 79 20 76 61 6c 75 65 3a 0d 0d 42 69 |inary value:..Bi| 00000670 74 20 31 20 73 74 61 74 65 20 20 42 69 74 20 32 |t 1 state Bit 2| 00000680 20 73 74 61 74 65 20 20 42 69 74 20 33 20 73 74 | state Bit 3 st| 00000690 61 74 65 20 20 42 69 74 20 34 20 73 74 61 74 65 |ate Bit 4 state| 000006a0 20 20 43 6f 6c 6f 75 72 20 20 44 65 66 61 75 6c | Colour Defaul| 000006b0 74 0d 20 20 30 20 20 20 20 20 20 20 20 20 20 20 |t. 0 | 000006c0 20 30 20 20 20 20 20 20 20 20 20 20 20 20 30 20 | 0 0 | 000006d0 20 20 20 20 20 20 20 20 20 20 20 30 20 20 20 20 | 0 | 000006e0 20 20 20 20 20 20 20 20 30 20 20 20 20 20 20 20 | 0 | 000006f0 42 4c 4b 0d 20 20 31 20 20 20 20 20 20 20 20 20 |BLK. 1 | 00000700 20 20 20 30 20 20 20 20 20 20 20 20 20 20 20 20 | 0 | 00000710 30 20 20 20 20 20 20 20 20 20 20 20 20 30 20 20 |0 0 | 00000720 20 20 20 20 20 20 20 20 20 20 31 20 20 20 20 20 | 1 | 00000730 20 20 52 45 44 0d 20 20 30 20 20 20 20 20 20 20 | RED. 0 | 00000740 20 20 20 20 20 31 20 20 20 20 20 20 20 20 20 20 | 1 | 00000750 20 20 30 20 20 20 20 20 20 20 20 20 20 20 20 30 | 0 0| 00000760 20 20 20 20 20 20 20 20 20 20 20 20 32 20 20 20 | 2 | 00000770 20 20 20 20 47 52 4e 0d 20 20 31 20 20 20 20 20 | GRN. 1 | 00000780 20 20 20 20 20 20 20 31 20 20 20 20 20 20 20 20 | 1 | 00000790 20 20 20 20 30 20 20 20 20 20 20 20 20 20 20 20 | 0 | 000007a0 20 30 20 20 20 20 20 20 20 20 20 20 20 20 33 20 | 0 3 | 000007b0 20 20 20 20 20 20 59 45 4c 0d 20 20 30 20 20 20 | YEL. 0 | 000007c0 20 20 20 20 20 20 20 20 20 30 20 20 20 20 20 20 | 0 | 000007d0 20 20 20 20 20 20 31 20 20 20 20 20 20 20 20 20 | 1 | 000007e0 20 20 20 30 20 20 20 20 20 20 20 20 20 20 20 20 | 0 | 000007f0 34 20 20 20 20 20 20 20 42 4c 45 0d 20 20 31 20 |4 BLE. 1 | 00000800 20 20 20 20 20 20 20 20 20 20 20 30 20 20 20 20 | 0 | 00000810 20 20 20 20 20 20 20 20 31 20 20 20 20 20 20 20 | 1 | 00000820 20 20 20 20 20 30 20 20 20 20 20 20 20 20 20 20 | 0 | 00000830 20 20 35 20 20 20 20 20 20 20 4d 47 4e 0d 20 20 | 5 MGN. | 00000840 30 20 20 20 20 20 20 20 20 20 20 20 20 31 20 20 |0 1 | 00000850 20 20 20 20 20 20 20 20 20 20 31 20 20 20 20 20 | 1 | 00000860 20 20 20 20 20 20 20 30 20 20 20 20 20 20 20 20 | 0 | 00000870 20 20 20 20 36 20 20 20 20 20 20 20 43 59 4e 0d | 6 CYN.| 00000880 20 20 31 20 20 20 20 20 20 20 20 20 20 20 20 31 | 1 1| 00000890 20 20 20 20 20 20 20 20 20 20 20 20 31 20 20 20 | 1 | 000008a0 20 20 20 20 20 20 20 20 20 30 20 20 20 20 20 20 | 0 | 000008b0 20 20 20 20 20 20 37 20 20 20 20 20 20 20 57 48 | 7 WH| 000008c0 54 0d 20 20 30 20 20 20 20 20 20 20 20 20 20 20 |T. 0 | 000008d0 20 30 20 20 20 20 20 20 20 20 20 20 20 20 30 20 | 0 0 | 000008e0 20 20 20 20 20 20 20 20 20 20 20 31 20 20 20 20 | 1 | 000008f0 20 20 20 20 20 20 20 20 38 20 20 20 20 20 42 4c | 8 BL| 00000900 4b 2f 57 48 54 0d 20 20 31 20 20 20 20 20 20 20 |K/WHT. 1 | 00000910 20 20 20 20 20 30 20 20 20 20 20 20 20 20 20 20 | 0 | 00000920 20 20 30 20 20 20 20 20 20 20 20 20 20 20 20 31 | 0 1| 00000930 20 20 20 20 20 20 20 20 20 20 20 20 39 20 20 20 | 9 | 00000940 20 20 52 45 44 2f 43 59 4e 0d 20 20 30 20 20 20 | RED/CYN. 0 | 00000950 20 20 20 20 20 20 20 20 20 31 20 20 20 20 20 20 | 1 | 00000960 20 20 20 20 20 20 30 20 20 20 20 20 20 20 20 20 | 0 | 00000970 20 20 20 31 20 20 20 20 20 20 20 20 20 20 20 31 | 1 1| 00000980 30 20 20 20 20 20 47 52 4e 2f 4d 47 4e 0d 20 20 |0 GRN/MGN. | 00000990 31 20 20 20 20 20 20 20 20 20 20 20 20 31 20 20 |1 1 | 000009a0 20 20 20 20 20 20 20 20 20 20 30 20 20 20 20 20 | 0 | 000009b0 20 20 20 20 20 20 20 31 20 20 20 20 20 20 20 20 | 1 | 000009c0 20 20 20 31 31 20 20 20 20 20 59 45 4c 2f 42 4c | 11 YEL/BL| 000009d0 45 0d 20 20 30 20 20 20 20 20 20 20 20 20 20 20 |E. 0 | 000009e0 20 30 20 20 20 20 20 20 20 20 20 20 20 20 31 20 | 0 1 | 000009f0 20 20 20 20 20 20 20 20 20 20 20 31 20 20 20 20 | 1 | 00000a00 20 20 20 20 20 20 20 31 32 20 20 20 20 20 42 4c | 12 BL| 00000a10 45 2f 59 45 4c 0d 20 20 31 20 20 20 20 20 20 20 |E/YEL. 1 | 00000a20 20 20 20 20 20 30 20 20 20 20 20 20 20 20 20 20 | 0 | 00000a30 20 20 31 20 20 20 20 20 20 20 20 20 20 20 20 31 | 1 1| 00000a40 20 20 20 20 20 20 20 20 20 20 20 31 33 20 20 20 | 13 | 00000a50 20 20 4d 47 4e 2f 47 52 4e 0d 20 20 30 20 20 20 | MGN/GRN. 0 | 00000a60 20 20 20 20 20 20 20 20 20 31 20 20 20 20 20 20 | 1 | 00000a70 20 20 20 20 20 20 31 20 20 20 20 20 20 20 20 20 | 1 | 00000a80 20 20 20 31 20 20 20 20 20 20 20 20 20 20 20 31 | 1 1| 00000a90 34 20 20 20 20 20 43 59 4e 2f 52 45 44 0d 20 20 |4 CYN/RED. | 00000aa0 31 20 20 20 20 20 20 20 20 20 20 20 20 31 20 20 |1 1 | 00000ab0 20 20 20 20 20 20 20 20 20 20 31 20 20 20 20 20 | 1 | 00000ac0 20 20 20 20 20 20 20 31 20 20 20 20 20 20 20 20 | 1 | 00000ad0 20 20 20 31 35 20 20 20 20 20 57 48 54 2f 42 4c | 15 WHT/BL| 00000ae0 4b 0d 0d 5b 44 65 66 61 75 6c 74 3a 20 44 65 66 |K..[Default: Def| 00000af0 61 75 6c 74 20 73 65 74 74 69 6e 67 20 6f 66 20 |ault setting of | 00000b00 74 68 69 73 20 6c 6f 67 69 63 61 6c 20 63 6f 6c |this logical col| 00000b10 6f 75 72 20 77 68 65 6e 20 4d 4f 44 45 20 32 20 |our when MODE 2 | 00000b20 69 73 20 66 69 72 73 74 0d 65 6e 74 65 72 65 64 |is first.entered| 00000b30 5d 0d 53 6f 2e 2e 2e 20 74 68 65 20 45 6c 65 63 |].So... the Elec| 00000b40 74 72 6f 6e 20 68 61 73 20 6d 6f 64 65 73 20 77 |tron has modes w| 00000b50 68 65 72 65 20 74 68 65 20 64 65 66 69 6e 69 74 |here the definit| 00000b60 69 6f 6e 20 6f 66 20 74 68 65 20 63 6f 6c 6f 75 |ion of the colou| 00000b70 72 20 6f 66 20 61 0d 63 65 72 74 61 69 6e 20 70 |r of a.certain p| 00000b80 69 78 65 6c 20 63 61 6e 20 74 61 6b 65 20 31 2c |ixel can take 1,| 00000b90 20 32 20 6f 72 20 34 20 62 69 74 73 2e 20 41 73 | 2 or 4 bits. As| 00000ba0 20 65 61 63 68 20 62 79 74 65 20 6f 66 20 74 68 | each byte of th| 00000bb0 65 20 65 6c 65 63 74 72 6f 6e 27 73 0d 6d 65 6d |e electron's.mem| 00000bc0 6f 72 79 20 63 6f 6e 73 69 73 74 73 20 6f 66 20 |ory consists of | 00000bd0 38 20 73 65 70 65 72 61 74 65 20 62 69 74 73 2c |8 seperate bits,| 00000be0 20 74 68 69 73 20 6d 65 61 6e 73 20 74 68 61 74 | this means that| 00000bf0 20 69 6e 20 6d 6f 6e 6f 63 68 72 6f 6d 65 20 6d | in monochrome m| 00000c00 6f 64 65 73 0d 77 65 20 63 61 6e 20 66 69 74 20 |odes.we can fit | 00000c10 38 20 70 69 78 65 6c 73 20 69 6e 74 6f 20 65 61 |8 pixels into ea| 00000c20 63 68 20 62 79 74 65 20 28 38 2f 31 3d 38 29 2e |ch byte (8/1=8).| 00000c30 20 49 6e 20 66 6f 75 72 20 63 6f 6c 6f 75 72 20 | In four colour | 00000c40 6d 6f 64 65 73 20 28 77 68 65 72 65 0d 65 61 63 |modes (where.eac| 00000c50 68 20 70 69 78 65 6c 20 72 65 71 75 69 72 65 73 |h pixel requires| 00000c60 20 74 77 6f 20 62 69 74 73 29 20 77 65 20 63 61 | two bits) we ca| 00000c70 6e 20 66 69 74 20 34 20 70 69 78 65 6c 73 20 69 |n fit 4 pixels i| 00000c80 6e 74 6f 20 65 61 63 68 20 62 79 74 65 20 28 38 |nto each byte (8| 00000c90 2f 32 3d 34 29 2e 0d 46 69 6e 61 6c 6c 79 20 69 |/2=4)..Finally i| 00000ca0 6e 20 4d 4f 44 45 20 32 20 28 74 68 65 20 73 69 |n MODE 2 (the si| 00000cb0 78 74 65 65 6e 20 63 6f 6c 6f 75 72 20 6d 6f 64 |xteen colour mod| 00000cc0 65 20 77 68 65 72 65 20 65 61 63 68 20 70 69 78 |e where each pix| 00000cd0 65 6c 20 72 65 71 75 69 72 65 73 20 34 0d 62 69 |el requires 4.bi| 00000ce0 74 73 29 20 77 65 20 63 61 6e 20 66 69 74 20 74 |ts) we can fit t| 00000cf0 77 6f 20 70 69 78 65 6c 73 20 69 6e 74 6f 20 65 |wo pixels into e| 00000d00 61 63 68 20 62 79 74 65 2e 20 4c 65 74 27 73 20 |ach byte. Let's | 00000d10 6e 6f 77 20 6c 6f 6f 6b 20 61 74 20 68 6f 77 20 |now look at how | 00000d20 65 61 63 68 20 69 73 0d 6c 61 69 64 20 6f 75 74 |each is.laid out| 00000d30 20 69 6e 20 6d 6f 72 65 20 64 65 70 74 68 3a 0d | in more depth:.| 00000d40 0d 4d 4f 4e 4f 43 48 52 4f 4d 45 20 4d 4f 44 45 |.MONOCHROME MODE| 00000d50 53 3a 0d 0d 54 68 65 73 65 20 61 72 65 20 6c 61 |S:..These are la| 00000d60 69 64 20 6f 75 74 20 69 6e 20 74 68 65 20 73 69 |id out in the si| 00000d70 6d 70 6c 65 73 74 20 77 61 79 2c 20 61 73 20 65 |mplest way, as e| 00000d80 69 67 68 74 20 70 69 78 65 6c 73 20 66 69 74 20 |ight pixels fit | 00000d90 69 6e 74 6f 20 65 61 63 68 0d 62 79 74 65 2e 20 |into each.byte. | 00000da0 54 68 65 20 63 68 61 72 61 63 74 65 72 2c 20 72 |The character, r| 00000db0 65 6d 65 6d 62 65 72 2c 20 63 6f 6e 73 69 73 74 |emember, consist| 00000dc0 73 20 6f 66 20 61 6e 20 38 2d 62 79 2d 38 20 73 |s of an 8-by-8 s| 00000dd0 71 75 61 72 65 20 6f 66 20 70 69 78 65 6c 73 2e |quare of pixels.| 00000de0 20 54 68 65 0d 64 61 74 61 20 69 73 20 73 74 6f | The.data is sto| 00000df0 72 65 64 20 69 6e 20 74 68 65 20 73 61 6d 65 20 |red in the same | 00000e00 77 61 79 20 61 73 20 75 73 65 72 20 64 65 66 69 |way as user defi| 00000e10 6e 65 64 20 63 68 61 72 61 63 74 65 72 73 20 61 |ned characters a| 00000e20 72 65 20 64 65 66 69 6e 65 64 0d 75 73 69 6e 67 |re defined.using| 00000e30 20 56 44 55 20 32 33 2e 20 54 68 65 20 66 69 72 | VDU 23. The fir| 00000e40 73 74 20 62 79 74 65 20 6f 66 20 74 68 65 20 64 |st byte of the d| 00000e50 65 66 69 6e 69 74 69 6f 6e 20 64 65 66 69 6e 65 |efinition define| 00000e60 73 20 74 68 65 20 74 6f 70 20 72 6f 77 20 6f 66 |s the top row of| 00000e70 0d 65 69 67 68 74 20 70 69 78 65 6c 73 3b 20 74 |.eight pixels; t| 00000e80 68 65 20 73 65 63 6f 6e 64 20 64 65 66 69 6e 65 |he second define| 00000e90 73 20 74 68 65 20 73 65 63 6f 6e 64 20 72 6f 77 |s the second row| 00000ea0 20 64 6f 77 6e 2c 20 65 74 63 2e 20 54 68 75 73 | down, etc. Thus| 00000eb0 20 74 68 65 20 65 6e 74 69 72 65 0d 63 68 61 72 | the entire.char| 00000ec0 61 63 74 65 72 20 63 61 6e 20 62 65 20 64 65 66 |acter can be def| 00000ed0 69 6e 65 64 20 69 6e 20 65 69 67 68 74 20 62 79 |ined in eight by| 00000ee0 74 65 73 2c 20 61 6e 64 20 74 68 69 73 20 69 73 |tes, and this is| 00000ef0 20 74 68 65 20 6e 75 6d 62 65 72 20 6f 66 20 62 | the number of b| 00000f00 79 74 65 73 0d 6f 66 20 74 68 65 20 45 6c 6b 27 |ytes.of the Elk'| 00000f10 73 20 6d 65 6d 6f 72 79 20 77 68 69 63 68 20 69 |s memory which i| 00000f20 73 20 75 73 65 64 20 62 79 20 65 61 63 68 20 63 |s used by each c| 00000f30 68 61 72 61 63 74 65 72 27 73 20 64 65 66 69 6e |haracter's defin| 00000f40 69 74 69 6f 6e 2e 20 4e 6f 74 65 20 2d 0d 74 68 |ition. 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