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V/+ADDRES
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_50.ADF |
| Filename: | V/+ADDRES |
| Read OK: | ✔ |
| File size: | 0EA3 bytes |
| Load address: | 56204556 |
| Exec address: | 44412B2E |
Duplicates
There are 2 duplicate copies of this file in the archive:
- AEW website » eug » eug_3_5_discs_Eug-50_A-EUG50.adf » V/+ADDRES
- AEW website » eug » eug_5_25_discs_Eug-50_D-EUG50.dsd » V.+ADDRES
- Personal collection » Acorn ADFS disks » Electron_User_Group » EUG_50.ADF » V/+ADDRES
File contents
24bBC ADDRESS BUS AND 8MB RAM DISK
By Robert Sprowson
THE limited expansion capabilities of an 8 bit addon on the 1MHz con-
nector on the BBC micro are easily overcome with some latches.
A fully decoded 24 bit address bus is presented here, giving up to 16
million unique locations! Half of this (8Mb) has been allocated as RAM
for a fast RAM disk.
It's up to the user's imagination to decide what input/output devices
are connected to the other 8 million locations - some suggestions are a
real time clock, your favourite ROM images, extra serial/parallel ports,
a TV card, etc...
Parts
THE slideshow of circuit diagrams in the Utilities Menu show how to
assemble the unit electrically. It requires the following parts:
3 x 74LS373 latches
3 x 74LS241 tristate buffers
4 x 74LS02
1 x 74LS00
1 x 4075BE
1 x 470uF capacitor
6 x 33nF capacitors
1 x 34 way IDC connector,and ribbon cable
2 x 3.3k resistor packs (8 resistors to a pack)
1 x stripboard,solder,and wires
In addition, the prototype RAM disk used 2 x 628128 SRAM chips (i.e.
256k in total), though any combination up to 8Mb can be added with a
little extra circuitry.
Benefits
* Single board decodes and cleans up all the 1MHz bus signals making
future projects easier to build
* Can be mounted internally to the case
* Use of a diode and 4.5v battery makes the RAM disk permanent
* No more grinding of precious floppy disks
* Fully featured RAM filing system already available
How To Build
1. Carefully consult the circuit diagram and manufacturers' data sheets
for the logic ICs, to arrive at a strip board layout.
2. Be sure to terminate the data bus with 3.3k resistors to 5v and 0v to
stop reflections over long cable lengths.
3. The decoupling capacitors (33nF) should be mounted as close to the
latch and tristate buffers as possible to stop noise on the power
lines.
4. It's arbitary which latches and tristate buffers you use for each of
the eight data lines from the BBC,but be consistent and label the
final board!
5. The RAM chips are best mounted on a small 'daughter' board as this
makes the wiring from the latches to the RAM address lines easier -
busses are very hard to implement on stripboard.
6. It's arbitary which order the RAM address lines are joined to the
main board since bytes will be read back from the same place they
were written, so it doesn't matter.
7. The board should be attached to a regulated supply capable of
supplying about 250mA.
Hints
* Below around 2.5v the contents of SRAM may become corrupted or lost.
* You can dramatically reduce the number of chips you need and (more
so) the wiring between the chips by use of 74ALS990 read/write
buffers.
* The board appears at &FC00, &FC01, &FC02 for the three address reg-
isters which is the 'test hardware' allocation in the 1MHz bus memory
map. Read/writes to the RAM occur at &FC03.
* The use of both latches and read back tristate buffers makes
?&FC00=?&FC00+1 in BASIC possible, or INC&FC00 in assembler which
have great speed increases over having to keep copies of the reg-
isters in the BBC's RAM
* Interrupt routines concerned with hardware on the 24bBC board must
preserve the current address by reading FC00/01/02,and restoring this
before exiting.
Happy soldering!
Robert Sprowson
IF you're not confident enough to build this piece of hardware yourself,
Robert Sprowson is offering a ready-made board service. Read his letter
from the Letters Menu for more details.
(The) Dave
00000000 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 | | 00000010 20 20 32 34 62 42 43 20 41 44 44 52 45 53 53 20 | 24bBC ADDRESS | 00000020 42 55 53 20 41 4e 44 20 38 4d 42 20 52 41 4d 20 |BUS AND 8MB RAM | 00000030 44 49 53 4b 0d 20 20 20 20 20 20 20 20 20 20 20 |DISK. | 00000040 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 42 | B| 00000050 79 20 52 6f 62 65 72 74 20 53 70 72 6f 77 73 6f |y Robert Sprowso| 00000060 6e 0d 0d 54 48 45 20 6c 69 6d 69 74 65 64 20 65 |n..THE limited e| 00000070 78 70 61 6e 73 69 6f 6e 20 63 61 70 61 62 69 6c |xpansion capabil| 00000080 69 74 69 65 73 20 6f 66 20 61 6e 20 38 20 62 69 |ities of an 8 bi| 00000090 74 20 61 64 64 6f 6e 20 6f 6e 20 74 68 65 20 31 |t addon on the 1| 000000a0 4d 48 7a 20 63 6f 6e 2d 0d 6e 65 63 74 6f 72 20 |MHz con-.nector | 000000b0 6f 6e 20 74 68 65 20 42 42 43 20 6d 69 63 72 6f |on the BBC micro| 000000c0 20 61 72 65 20 65 61 73 69 6c 79 20 6f 76 65 72 | are easily over| 000000d0 63 6f 6d 65 20 77 69 74 68 20 73 6f 6d 65 20 6c |come with some l| 000000e0 61 74 63 68 65 73 2e 0d 20 20 20 41 20 66 75 6c |atches.. A ful| 000000f0 6c 79 20 64 65 63 6f 64 65 64 20 32 34 20 62 69 |ly decoded 24 bi| 00000100 74 20 61 64 64 72 65 73 73 20 62 75 73 20 69 73 |t address bus is| 00000110 20 70 72 65 73 65 6e 74 65 64 20 68 65 72 65 2c | presented here,| 00000120 20 67 69 76 69 6e 67 20 75 70 20 74 6f 20 31 36 | giving up to 16| 00000130 0d 6d 69 6c 6c 69 6f 6e 20 75 6e 69 71 75 65 20 |.million unique | 00000140 6c 6f 63 61 74 69 6f 6e 73 21 20 48 61 6c 66 20 |locations! Half | 00000150 6f 66 20 74 68 69 73 20 28 38 4d 62 29 20 68 61 |of this (8Mb) ha| 00000160 73 20 62 65 65 6e 20 61 6c 6c 6f 63 61 74 65 64 |s been allocated| 00000170 20 61 73 20 52 41 4d 0d 66 6f 72 20 61 20 66 61 | as RAM.for a fa| 00000180 73 74 20 52 41 4d 20 64 69 73 6b 2e 0d 20 20 20 |st RAM disk.. | 00000190 49 74 27 73 20 75 70 20 74 6f 20 74 68 65 20 75 |It's up to the u| 000001a0 73 65 72 27 73 20 69 6d 61 67 69 6e 61 74 69 6f |ser's imaginatio| 000001b0 6e 20 74 6f 20 64 65 63 69 64 65 20 77 68 61 74 |n to decide what| 000001c0 20 69 6e 70 75 74 2f 6f 75 74 70 75 74 20 64 65 | input/output de| 000001d0 76 69 63 65 73 0d 61 72 65 20 63 6f 6e 6e 65 63 |vices.are connec| 000001e0 74 65 64 20 74 6f 20 74 68 65 20 6f 74 68 65 72 |ted to the other| 000001f0 20 38 20 6d 69 6c 6c 69 6f 6e 20 6c 6f 63 61 74 | 8 million locat| 00000200 69 6f 6e 73 20 2d 20 73 6f 6d 65 20 73 75 67 67 |ions - some sugg| 00000210 65 73 74 69 6f 6e 73 20 61 72 65 20 61 0d 72 65 |estions are a.re| 00000220 61 6c 20 74 69 6d 65 20 63 6c 6f 63 6b 2c 20 79 |al time clock, y| 00000230 6f 75 72 20 66 61 76 6f 75 72 69 74 65 20 52 4f |our favourite RO| 00000240 4d 20 69 6d 61 67 65 73 2c 20 65 78 74 72 61 20 |M images, extra | 00000250 73 65 72 69 61 6c 2f 70 61 72 61 6c 6c 65 6c 20 |serial/parallel | 00000260 70 6f 72 74 73 2c 0d 61 20 54 56 20 63 61 72 64 |ports,.a TV card| 00000270 2c 20 65 74 63 2e 2e 2e 0d 0d 50 61 72 74 73 0d |, etc.....Parts.| 00000280 54 48 45 20 73 6c 69 64 65 73 68 6f 77 20 6f 66 |THE slideshow of| 00000290 20 63 69 72 63 75 69 74 20 64 69 61 67 72 61 6d | circuit diagram| 000002a0 73 20 69 6e 20 74 68 65 20 55 74 69 6c 69 74 69 |s in the Utiliti| 000002b0 65 73 20 4d 65 6e 75 20 73 68 6f 77 20 68 6f 77 |es Menu show how| 000002c0 20 74 6f 20 0d 61 73 73 65 6d 62 6c 65 20 74 68 | to .assemble th| 000002d0 65 20 75 6e 69 74 20 65 6c 65 63 74 72 69 63 61 |e unit electrica| 000002e0 6c 6c 79 2e 20 49 74 20 72 65 71 75 69 72 65 73 |lly. It requires| 000002f0 20 74 68 65 20 66 6f 6c 6c 6f 77 69 6e 67 20 70 | the following p| 00000300 61 72 74 73 3a 0d 20 20 20 33 20 20 78 20 20 37 |arts:. 3 x 7| 00000310 34 4c 53 33 37 33 20 6c 61 74 63 68 65 73 0d 20 |4LS373 latches. | 00000320 20 20 33 20 20 78 20 20 37 34 4c 53 32 34 31 20 | 3 x 74LS241 | 00000330 74 72 69 73 74 61 74 65 20 62 75 66 66 65 72 73 |tristate buffers| 00000340 0d 20 20 20 34 20 20 78 20 20 37 34 4c 53 30 32 |. 4 x 74LS02| 00000350 0d 20 20 20 31 20 20 78 20 20 37 34 4c 53 30 30 |. 1 x 74LS00| 00000360 0d 20 20 20 31 20 20 78 20 20 34 30 37 35 42 45 |. 1 x 4075BE| 00000370 0d 20 20 20 31 20 20 78 20 20 34 37 30 75 46 20 |. 1 x 470uF | 00000380 63 61 70 61 63 69 74 6f 72 0d 20 20 20 36 20 20 |capacitor. 6 | 00000390 78 20 20 33 33 6e 46 20 63 61 70 61 63 69 74 6f |x 33nF capacito| 000003a0 72 73 0d 20 20 20 31 20 20 78 20 20 33 34 20 77 |rs. 1 x 34 w| 000003b0 61 79 20 49 44 43 20 63 6f 6e 6e 65 63 74 6f 72 |ay IDC connector| 000003c0 2c 61 6e 64 20 72 69 62 62 6f 6e 20 63 61 62 6c |,and ribbon cabl| 000003d0 65 0d 20 20 20 32 20 20 78 20 20 33 2e 33 6b 20 |e. 2 x 3.3k | 000003e0 72 65 73 69 73 74 6f 72 20 70 61 63 6b 73 20 28 |resistor packs (| 000003f0 38 20 72 65 73 69 73 74 6f 72 73 20 74 6f 20 61 |8 resistors to a| 00000400 20 70 61 63 6b 29 0d 20 20 20 31 20 20 78 20 20 | pack). 1 x | 00000410 73 74 72 69 70 62 6f 61 72 64 2c 73 6f 6c 64 65 |stripboard,solde| 00000420 72 2c 61 6e 64 20 77 69 72 65 73 0d 0d 49 6e 20 |r,and wires..In | 00000430 61 64 64 69 74 69 6f 6e 2c 20 74 68 65 20 70 72 |addition, the pr| 00000440 6f 74 6f 74 79 70 65 20 52 41 4d 20 64 69 73 6b |ototype RAM disk| 00000450 20 75 73 65 64 20 32 20 78 20 36 32 38 31 32 38 | used 2 x 628128| 00000460 20 53 52 41 4d 20 63 68 69 70 73 20 28 69 2e 65 | SRAM chips (i.e| 00000470 2e 20 0d 32 35 36 6b 20 69 6e 20 74 6f 74 61 6c |. .256k in total| 00000480 29 2c 20 74 68 6f 75 67 68 20 61 6e 79 20 63 6f |), though any co| 00000490 6d 62 69 6e 61 74 69 6f 6e 20 75 70 20 74 6f 20 |mbination up to | 000004a0 38 4d 62 20 63 61 6e 20 62 65 20 61 64 64 65 64 |8Mb can be added| 000004b0 20 77 69 74 68 20 61 20 20 20 0d 6c 69 74 74 6c | with a .littl| 000004c0 65 20 65 78 74 72 61 20 63 69 72 63 75 69 74 72 |e extra circuitr| 000004d0 79 2e 0d 0d 42 65 6e 65 66 69 74 73 0d 2a 20 20 |y...Benefits.* | 000004e0 53 69 6e 67 6c 65 20 62 6f 61 72 64 20 64 65 63 |Single board dec| 000004f0 6f 64 65 73 20 61 6e 64 20 63 6c 65 61 6e 73 20 |odes and cleans | 00000500 75 70 20 61 6c 6c 20 74 68 65 20 31 4d 48 7a 20 |up all the 1MHz | 00000510 62 75 73 20 73 69 67 6e 61 6c 73 20 6d 61 6b 69 |bus signals maki| 00000520 6e 67 0d 20 20 20 66 75 74 75 72 65 20 70 72 6f |ng. future pro| 00000530 6a 65 63 74 73 20 65 61 73 69 65 72 20 74 6f 20 |jects easier to | 00000540 62 75 69 6c 64 0d 2a 20 20 43 61 6e 20 62 65 20 |build.* Can be | 00000550 6d 6f 75 6e 74 65 64 20 69 6e 74 65 72 6e 61 6c |mounted internal| 00000560 6c 79 20 74 6f 20 74 68 65 20 63 61 73 65 0d 2a |ly to the case.*| 00000570 20 20 55 73 65 20 6f 66 20 61 20 64 69 6f 64 65 | Use of a diode| 00000580 20 61 6e 64 20 34 2e 35 76 20 62 61 74 74 65 72 | and 4.5v batter| 00000590 79 20 6d 61 6b 65 73 20 74 68 65 20 52 41 4d 20 |y makes the RAM | 000005a0 64 69 73 6b 20 70 65 72 6d 61 6e 65 6e 74 0d 2a |disk permanent.*| 000005b0 20 20 4e 6f 20 6d 6f 72 65 20 67 72 69 6e 64 69 | No more grindi| 000005c0 6e 67 20 6f 66 20 70 72 65 63 69 6f 75 73 20 66 |ng of precious f| 000005d0 6c 6f 70 70 79 20 64 69 73 6b 73 0d 2a 20 20 46 |loppy disks.* F| 000005e0 75 6c 6c 79 20 66 65 61 74 75 72 65 64 20 52 41 |ully featured RA| 000005f0 4d 20 66 69 6c 69 6e 67 20 73 79 73 74 65 6d 20 |M filing system | 00000600 61 6c 72 65 61 64 79 20 61 76 61 69 6c 61 62 6c |already availabl| 00000610 65 0d 0d 48 6f 77 20 54 6f 20 42 75 69 6c 64 0d |e..How To Build.| 00000620 31 2e 20 43 61 72 65 66 75 6c 6c 79 20 63 6f 6e |1. Carefully con| 00000630 73 75 6c 74 20 74 68 65 20 63 69 72 63 75 69 74 |sult the circuit| 00000640 20 64 69 61 67 72 61 6d 20 61 6e 64 20 6d 61 6e | diagram and man| 00000650 75 66 61 63 74 75 72 65 72 73 27 20 64 61 74 61 |ufacturers' data| 00000660 20 73 68 65 65 74 73 0d 20 20 20 66 6f 72 20 74 | sheets. for t| 00000670 68 65 20 6c 6f 67 69 63 20 49 43 73 2c 20 74 6f |he logic ICs, to| 00000680 20 61 72 72 69 76 65 20 61 74 20 61 20 73 74 72 | arrive at a str| 00000690 69 70 20 62 6f 61 72 64 20 6c 61 79 6f 75 74 2e |ip board layout.| 000006a0 0d 32 2e 20 42 65 20 73 75 72 65 20 74 6f 20 74 |.2. Be sure to t| 000006b0 65 72 6d 69 6e 61 74 65 20 74 68 65 20 64 61 74 |erminate the dat| 000006c0 61 20 62 75 73 20 77 69 74 68 20 33 2e 33 6b 20 |a bus with 3.3k | 000006d0 72 65 73 69 73 74 6f 72 73 20 74 6f 20 35 76 20 |resistors to 5v | 000006e0 61 6e 64 20 30 76 20 74 6f 0d 20 20 20 73 74 6f |and 0v to. sto| 000006f0 70 20 72 65 66 6c 65 63 74 69 6f 6e 73 20 6f 76 |p reflections ov| 00000700 65 72 20 6c 6f 6e 67 20 63 61 62 6c 65 20 6c 65 |er long cable le| 00000710 6e 67 74 68 73 2e 0d 33 2e 20 54 68 65 20 64 65 |ngths..3. The de| 00000720 63 6f 75 70 6c 69 6e 67 20 63 61 70 61 63 69 74 |coupling capacit| 00000730 6f 72 73 20 28 33 33 6e 46 29 20 73 68 6f 75 6c |ors (33nF) shoul| 00000740 64 20 62 65 20 6d 6f 75 6e 74 65 64 20 61 73 20 |d be mounted as | 00000750 63 6c 6f 73 65 20 74 6f 20 74 68 65 20 0d 20 20 |close to the . | 00000760 20 6c 61 74 63 68 20 61 6e 64 20 74 72 69 73 74 | latch and trist| 00000770 61 74 65 20 62 75 66 66 65 72 73 20 61 73 20 70 |ate buffers as p| 00000780 6f 73 73 69 62 6c 65 20 74 6f 20 73 74 6f 70 20 |ossible to stop | 00000790 6e 6f 69 73 65 20 6f 6e 20 74 68 65 20 70 6f 77 |noise on the pow| 000007a0 65 72 0d 20 20 20 6c 69 6e 65 73 2e 0d 34 2e 20 |er. lines..4. | 000007b0 49 74 27 73 20 61 72 62 69 74 61 72 79 20 77 68 |It's arbitary wh| 000007c0 69 63 68 20 6c 61 74 63 68 65 73 20 61 6e 64 20 |ich latches and | 000007d0 74 72 69 73 74 61 74 65 20 62 75 66 66 65 72 73 |tristate buffers| 000007e0 20 79 6f 75 20 75 73 65 20 66 6f 72 20 65 61 63 | you use for eac| 000007f0 68 20 6f 66 20 0d 20 20 20 74 68 65 20 65 69 67 |h of . the eig| 00000800 68 74 20 64 61 74 61 20 6c 69 6e 65 73 20 66 72 |ht data lines fr| 00000810 6f 6d 20 74 68 65 20 42 42 43 2c 62 75 74 20 62 |om the BBC,but b| 00000820 65 20 63 6f 6e 73 69 73 74 65 6e 74 20 61 6e 64 |e consistent and| 00000830 20 6c 61 62 65 6c 20 74 68 65 0d 20 20 20 66 69 | label the. fi| 00000840 6e 61 6c 20 62 6f 61 72 64 21 0d 35 2e 20 54 68 |nal board!.5. Th| 00000850 65 20 52 41 4d 20 63 68 69 70 73 20 61 72 65 20 |e RAM chips are | 00000860 62 65 73 74 20 6d 6f 75 6e 74 65 64 20 6f 6e 20 |best mounted on | 00000870 61 20 73 6d 61 6c 6c 20 27 64 61 75 67 68 74 65 |a small 'daughte| 00000880 72 27 20 62 6f 61 72 64 20 61 73 20 74 68 69 73 |r' board as this| 00000890 20 0d 20 20 20 6d 61 6b 65 73 20 74 68 65 20 77 | . makes the w| 000008a0 69 72 69 6e 67 20 66 72 6f 6d 20 74 68 65 20 6c |iring from the l| 000008b0 61 74 63 68 65 73 20 74 6f 20 74 68 65 20 52 41 |atches to the RA| 000008c0 4d 20 61 64 64 72 65 73 73 20 6c 69 6e 65 73 20 |M address lines | 000008d0 65 61 73 69 65 72 20 2d 0d 20 20 20 62 75 73 73 |easier -. buss| 000008e0 65 73 20 61 72 65 20 76 65 72 79 20 68 61 72 64 |es are very hard| 000008f0 20 74 6f 20 69 6d 70 6c 65 6d 65 6e 74 20 6f 6e | to implement on| 00000900 20 73 74 72 69 70 62 6f 61 72 64 2e 0d 36 2e 20 | stripboard..6. | 00000910 49 74 27 73 20 61 72 62 69 74 61 72 79 20 77 68 |It's arbitary wh| 00000920 69 63 68 20 6f 72 64 65 72 20 74 68 65 20 52 41 |ich order the RA| 00000930 4d 20 61 64 64 72 65 73 73 20 6c 69 6e 65 73 20 |M address lines | 00000940 61 72 65 20 6a 6f 69 6e 65 64 20 74 6f 20 74 68 |are joined to th| 00000950 65 20 0d 20 20 20 6d 61 69 6e 20 62 6f 61 72 64 |e . main board| 00000960 20 73 69 6e 63 65 20 62 79 74 65 73 20 77 69 6c | since bytes wil| 00000970 6c 20 62 65 20 72 65 61 64 20 62 61 63 6b 20 66 |l be read back f| 00000980 72 6f 6d 20 74 68 65 20 73 61 6d 65 20 70 6c 61 |rom the same pla| 00000990 63 65 20 74 68 65 79 0d 20 20 20 77 65 72 65 20 |ce they. were | 000009a0 77 72 69 74 74 65 6e 2c 20 73 6f 20 69 74 20 64 |written, so it d| 000009b0 6f 65 73 6e 27 74 20 6d 61 74 74 65 72 2e 0d 37 |oesn't matter..7| 000009c0 2e 20 54 68 65 20 62 6f 61 72 64 20 73 68 6f 75 |. The board shou| 000009d0 6c 64 20 62 65 20 61 74 74 61 63 68 65 64 20 74 |ld be attached t| 000009e0 6f 20 61 20 72 65 67 75 6c 61 74 65 64 20 73 75 |o a regulated su| 000009f0 70 70 6c 79 20 63 61 70 61 62 6c 65 20 6f 66 0d |pply capable of.| 00000a00 20 20 20 73 75 70 70 6c 79 69 6e 67 20 61 62 6f | supplying abo| 00000a10 75 74 20 32 35 30 6d 41 2e 0d 0d 48 69 6e 74 73 |ut 250mA...Hints| 00000a20 0d 2a 20 20 42 65 6c 6f 77 20 61 72 6f 75 6e 64 |.* Below around| 00000a30 20 32 2e 35 76 20 74 68 65 20 63 6f 6e 74 65 6e | 2.5v the conten| 00000a40 74 73 20 6f 66 20 53 52 41 4d 20 6d 61 79 20 62 |ts of SRAM may b| 00000a50 65 63 6f 6d 65 20 63 6f 72 72 75 70 74 65 64 20 |ecome corrupted | 00000a60 6f 72 20 6c 6f 73 74 2e 0d 2a 20 20 59 6f 75 20 |or lost..* You | 00000a70 63 61 6e 20 64 72 61 6d 61 74 69 63 61 6c 6c 79 |can dramatically| 00000a80 20 72 65 64 75 63 65 20 74 68 65 20 6e 75 6d 62 | reduce the numb| 00000a90 65 72 20 6f 66 20 63 68 69 70 73 20 79 6f 75 20 |er of chips you | 00000aa0 6e 65 65 64 20 61 6e 64 20 28 6d 6f 72 65 20 0d |need and (more .| 00000ab0 20 20 20 73 6f 29 20 74 68 65 20 77 69 72 69 6e | so) the wirin| 00000ac0 67 20 62 65 74 77 65 65 6e 20 74 68 65 20 63 68 |g between the ch| 00000ad0 69 70 73 20 62 79 20 75 73 65 20 6f 66 20 37 34 |ips by use of 74| 00000ae0 41 4c 53 39 39 30 20 72 65 61 64 2f 77 72 69 74 |ALS990 read/writ| 00000af0 65 0d 20 20 20 62 75 66 66 65 72 73 2e 0d 2a 20 |e. buffers..* | 00000b00 20 54 68 65 20 62 6f 61 72 64 20 61 70 70 65 61 | The board appea| 00000b10 72 73 20 61 74 20 26 46 43 30 30 2c 20 26 46 43 |rs at &FC00, &FC| 00000b20 30 31 2c 20 26 46 43 30 32 20 66 6f 72 20 74 68 |01, &FC02 for th| 00000b30 65 20 74 68 72 65 65 20 61 64 64 72 65 73 73 20 |e three address | 00000b40 72 65 67 2d 0d 20 20 20 69 73 74 65 72 73 20 77 |reg-. isters w| 00000b50 68 69 63 68 20 69 73 20 74 68 65 20 27 74 65 73 |hich is the 'tes| 00000b60 74 20 68 61 72 64 77 61 72 65 27 20 61 6c 6c 6f |t hardware' allo| 00000b70 63 61 74 69 6f 6e 20 69 6e 20 74 68 65 20 31 4d |cation in the 1M| 00000b80 48 7a 20 62 75 73 20 6d 65 6d 6f 72 79 0d 20 20 |Hz bus memory. | 00000b90 20 6d 61 70 2e 20 52 65 61 64 2f 77 72 69 74 65 | map. Read/write| 00000ba0 73 20 74 6f 20 74 68 65 20 52 41 4d 20 6f 63 63 |s to the RAM occ| 00000bb0 75 72 20 61 74 20 26 46 43 30 33 2e 0d 2a 20 20 |ur at &FC03..* | 00000bc0 54 68 65 20 75 73 65 20 6f 66 20 62 6f 74 68 20 |The use of both | 00000bd0 6c 61 74 63 68 65 73 20 61 6e 64 20 72 65 61 64 |latches and read| 00000be0 20 62 61 63 6b 20 74 72 69 73 74 61 74 65 20 62 | back tristate b| 00000bf0 75 66 66 65 72 73 20 6d 61 6b 65 73 0d 20 20 20 |uffers makes. | 00000c00 3f 26 46 43 30 30 3d 3f 26 46 43 30 30 2b 31 20 |?&FC00=?&FC00+1 | 00000c10 69 6e 20 42 41 53 49 43 20 70 6f 73 73 69 62 6c |in BASIC possibl| 00000c20 65 2c 20 6f 72 20 49 4e 43 26 46 43 30 30 20 69 |e, or INC&FC00 i| 00000c30 6e 20 61 73 73 65 6d 62 6c 65 72 20 77 68 69 63 |n assembler whic| 00000c40 68 0d 20 20 20 68 61 76 65 20 67 72 65 61 74 20 |h. have great | 00000c50 73 70 65 65 64 20 69 6e 63 72 65 61 73 65 73 20 |speed increases | 00000c60 6f 76 65 72 20 68 61 76 69 6e 67 20 74 6f 20 6b |over having to k| 00000c70 65 65 70 20 63 6f 70 69 65 73 20 6f 66 20 74 68 |eep copies of th| 00000c80 65 20 72 65 67 2d 0d 20 20 20 69 73 74 65 72 73 |e reg-. isters| 00000c90 20 69 6e 20 74 68 65 20 42 42 43 27 73 20 52 41 | in the BBC's RA| 00000ca0 4d 0d 2a 20 20 49 6e 74 65 72 72 75 70 74 20 72 |M.* Interrupt r| 00000cb0 6f 75 74 69 6e 65 73 20 63 6f 6e 63 65 72 6e 65 |outines concerne| 00000cc0 64 20 77 69 74 68 20 68 61 72 64 77 61 72 65 20 |d with hardware | 00000cd0 6f 6e 20 74 68 65 20 32 34 62 42 43 20 62 6f 61 |on the 24bBC boa| 00000ce0 72 64 20 6d 75 73 74 0d 20 20 20 70 72 65 73 65 |rd must. prese| 00000cf0 72 76 65 20 74 68 65 20 63 75 72 72 65 6e 74 20 |rve the current | 00000d00 61 64 64 72 65 73 73 20 62 79 20 72 65 61 64 69 |address by readi| 00000d10 6e 67 20 46 43 30 30 2f 30 31 2f 30 32 2c 61 6e |ng FC00/01/02,an| 00000d20 64 20 72 65 73 74 6f 72 69 6e 67 20 74 68 69 73 |d restoring this| 00000d30 0d 20 20 20 62 65 66 6f 72 65 20 65 78 69 74 69 |. before exiti| 00000d40 6e 67 2e 0d 0d 48 61 70 70 79 20 73 6f 6c 64 65 |ng...Happy solde| 00000d50 72 69 6e 67 21 20 0d 20 20 20 20 20 20 20 20 20 |ring! . | 00000d60 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 | | * 00000d90 52 6f 62 65 72 74 20 53 70 72 6f 77 73 6f 6e 0d |Robert Sprowson.| 00000da0 0d 49 46 20 79 6f 75 27 72 65 20 6e 6f 74 20 63 |.IF you're not c| 00000db0 6f 6e 66 69 64 65 6e 74 20 65 6e 6f 75 67 68 20 |onfident enough | 00000dc0 74 6f 20 62 75 69 6c 64 20 74 68 69 73 20 70 69 |to build this pi| 00000dd0 65 63 65 20 6f 66 20 68 61 72 64 77 61 72 65 20 |ece of hardware | 00000de0 79 6f 75 72 73 65 6c 66 2c 0d 52 6f 62 65 72 74 |yourself,.Robert| 00000df0 20 53 70 72 6f 77 73 6f 6e 20 69 73 20 6f 66 66 | Sprowson is off| 00000e00 65 72 69 6e 67 20 61 20 72 65 61 64 79 2d 6d 61 |ering a ready-ma| 00000e10 64 65 20 62 6f 61 72 64 20 73 65 72 76 69 63 65 |de board service| 00000e20 2e 20 52 65 61 64 20 68 69 73 20 6c 65 74 74 65 |. Read his lette| 00000e30 72 0d 66 72 6f 6d 20 74 68 65 20 4c 65 74 74 65 |r.from the Lette| 00000e40 72 73 20 4d 65 6e 75 20 66 6f 72 20 6d 6f 72 65 |rs Menu for more| 00000e50 20 64 65 74 61 69 6c 73 2e 0d 20 20 20 20 20 20 | details.. | 00000e60 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 | | * 00000e90 20 20 20 20 20 20 20 20 28 54 68 65 29 20 44 61 | (The) Da| 00000ea0 76 65 0d |ve.| 00000ea3
V/+ADDRES.m0
V/+ADDRES.m1
V/+ADDRES.m2
V/+ADDRES.m4
V/+ADDRES.m5
.