Home » Personal collection » Acorn ADFS disks » Electron_User_Group » EUG_51.ADF » V/+SERROM

V/+SERROM

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_51.ADF
Filename: V/+SERROM
Read OK: ✔
File size: 1AD7 bytes
Load address: 2B204556
Exec address: 52524553
Duplicates

There are 2 duplicate copies of this file in the archive:

File contents
                     EXAMPLE SERVICE ROM HEADER

THIS piece of source code is ONLY for advanced 6502 programmers or users
wishing to create their own Paged ROMs. The explanation following is
quite technical so if you require further information then contact EUG
and any queries will be passed on.
   This source code demonstrates a simple way of making a robust Paged
ROM that can either be loaded into Sideways RAM or blown onto an EPROM.
The code has been designed not for compactness or optimisation, but to
allow easy implantation of extra commands and readability. (When I first
started writing ROMs, I used to write custom headers, which always made
updates difficult to implement and error-prone.) Some coders will look 
at this code and frown at the use of what seems like unnecessary JMP 
instructions. However, it is specifically written in such a way that
each code section is totally independent of each other and thus code and
data can be implanted anywhere without any relatives moving out of 
range. (Goodbyte BYTE errors!)
   Advanced ROM coders should not that this header example does NOT 
support Autoboot, Private Workspace Claims or Claims of the NMI Work-
space or zero-page locations. If you require these service calls, you
should implant/intercept them in the Service Entry part of the source
code. (Not forgetting to add release claims also!!!)
   The first part of the code consists of a standard ROM header, as used
by all Paged ROMs. (Please note that I have removed the bug in the 
header that the Acorn Electron Advanced User Guide contains!!) The ROM
title in this header is the text that is used to compare against and
printer when a *HELP command is received. However, altering this so that
another text string is used, is very easy and only requires changing one
EQUW statement. A portion of this text is also printed by the operating
system when a *ROMS command is issued.
   The Command Data is, as its name suggests, the commands that are
accepted by the Service ROM. All of this text between the labels .cdt 
and .cde is printed by the RON when a *HELP command is received with an
argument of the ROM title. *HELP with no arguments just yields the ROM
titles and version number. Each ROM command in this data block should
have its own label and be terminated with carriage return (&0D) for 
readability's sake when echoed to the screen. Please be aware that
lowercase to uppercase character conversion is used in the comparing of
issued commands (unrecognised commands that are offered to the Paged
ROMs) so please do not used weird characters or numbers in your command
names. Should you desperately require numbers in command names, you will
need to reqrite the Command Interpreter (and possibly the Help Inter-
preter also).
   The Service Entry is the piece of code called when the ROM is entered
and there is nothing complex about this code. It simply stores the ROM
entry registers and restores them on exit. The code only supports un-
recognised commands issued to the Paged ROMs and *HELP commands. As I
said earlier, if you ROM requires workspace or an NMI handler, you'll
need to add code here.
   I am actually open to debate on whether I should use zero-page 
locations (&70-&8F) as given to the user by BASIC. In actuality, your
ROM should probably reserve workspace, but I actually think that reser-
ving an entire page for just a few locations is very wasteful! I did 
think of grabbing the NMI and using its allocation of zero-page, but
another ROM could request the NMI workspace whilst this ROM was active.
The ROM would then be forced into relinquishing the NMI workspace and
you would again need some zero-page workspace!!
   The most important part of the source code is the Command Structure.
It is this data that defines what text is printed and checked for when
*HELP is issued and also how many and what commands the ROM actually 
has. The first entry in this table is the .hcs entry, which consists of
a byte that specifies how long the *HELP ROM title is, minus one. 
Following this is a 16 bit (word) pointer to the ROM title itself. It is
this text that will be used for comparison when a *HELP command is 
received with an argument of the ROM name.
   The .cms entry is where the command pointers are located. The first
byte is the number of ROM commands minus one. Each command entry con-
sists of five bytes. Therefore, if your ROM has four commands, your 
total .cms length would be (5 x 4) + 1. A command entry has a very sim
ple structure: A byte specifying the command length minus one, a word
pointer to the command name itself and a final word which is the JMP 
address in the Jump Table. Please be aware that a register is used to 
step through this Command Structure and therefore the number of possible
commands is limited to a maximum of 85. With careful reprogramming using
indirect addressing, it would be possible to increase this, but I would
have though that 85 was sufficient!!
   The Jump Array comes next. This might be considered by some program-
mers to be superfluous when the command structure could achieve the same
results. Well, I thought about this and since everything in this header
is very modular, a jump table was a much neater way of achieving order.
   The Help Interpreter is the code called when a *HELP command is
issued. It first scans the CLI looking for arguments and if none are 
found simply reports the ROM name and version number. However, if the
supplied argument matches the text pointed to by the .hcs pointer, then
the ROM command list is echoed to the screen. Character conversion is
performed on the input stream so that character case is equal. Please be
aware of this if you are planning on using any strange characters.
   The Command Interpreter is roughly the same as the Help Interpreter.
Character case conversion is done on the input stream so special char-
acters may cause commands to not be recognised. It scans the Command
Structure for as many commands as indicated and, when one is recognised,
it clears location (&70) which is the Accumulator of the ROM exit value.
If you are writing a large ROM with many commands, please take care that
the Command Structure does not exceed a Page in length! As warned  
earlier, the Command Structure is stepped through using a register and
is therefore limited to 256 bytes.
   There are some points to note about this code. Firsty, no dodgy self-
modifying code is used at all. Secondly, it should work on any machine,
from all BBCs to the Acorn Electron with whatever expansions they may
have. Thirdly, when writing your ROM code, DO NOT use locations &70, &71
or &72 for storage. The other BASIC user locations (&73-&8F) may be used
as you see fit.
                                                         Chris Warburton
                                                      welder@majesty.net

00000000  20 20 20 20 20 20 20 20  20 20 20 20 20 20 20 20  |                |
00000010  20 20 20 20 20 45 58 41  4d 50 4c 45 20 53 45 52  |     EXAMPLE SER|
00000020  56 49 43 45 20 52 4f 4d  20 48 45 41 44 45 52 0d  |VICE ROM HEADER.|
00000030  0d 54 48 49 53 20 70 69  65 63 65 20 6f 66 20 73  |.THIS piece of s|
00000040  6f 75 72 63 65 20 63 6f  64 65 20 69 73 20 4f 4e  |ource code is ON|
00000050  4c 59 20 66 6f 72 20 61  64 76 61 6e 63 65 64 20  |LY for advanced |
00000060  36 35 30 32 20 70 72 6f  67 72 61 6d 6d 65 72 73  |6502 programmers|
00000070  20 6f 72 20 75 73 65 72  73 0d 77 69 73 68 69 6e  | or users.wishin|
00000080  67 20 74 6f 20 63 72 65  61 74 65 20 74 68 65 69  |g to create thei|
00000090  72 20 6f 77 6e 20 50 61  67 65 64 20 52 4f 4d 73  |r own Paged ROMs|
000000a0  2e 20 54 68 65 20 65 78  70 6c 61 6e 61 74 69 6f  |. The explanatio|
000000b0  6e 20 66 6f 6c 6c 6f 77  69 6e 67 20 69 73 0d 71  |n following is.q|
000000c0  75 69 74 65 20 74 65 63  68 6e 69 63 61 6c 20 73  |uite technical s|
000000d0  6f 20 69 66 20 79 6f 75  20 72 65 71 75 69 72 65  |o if you require|
000000e0  20 66 75 72 74 68 65 72  20 69 6e 66 6f 72 6d 61  | further informa|
000000f0  74 69 6f 6e 20 74 68 65  6e 20 63 6f 6e 74 61 63  |tion then contac|
00000100  74 20 45 55 47 0d 61 6e  64 20 61 6e 79 20 71 75  |t EUG.and any qu|
00000110  65 72 69 65 73 20 77 69  6c 6c 20 62 65 20 70 61  |eries will be pa|
00000120  73 73 65 64 20 6f 6e 2e  0d 20 20 20 54 68 69 73  |ssed on..   This|
00000130  20 73 6f 75 72 63 65 20  63 6f 64 65 20 64 65 6d  | source code dem|
00000140  6f 6e 73 74 72 61 74 65  73 20 61 20 73 69 6d 70  |onstrates a simp|
00000150  6c 65 20 77 61 79 20 6f  66 20 6d 61 6b 69 6e 67  |le way of making|
00000160  20 61 20 72 6f 62 75 73  74 20 50 61 67 65 64 0d  | a robust Paged.|
00000170  52 4f 4d 20 74 68 61 74  20 63 61 6e 20 65 69 74  |ROM that can eit|
00000180  68 65 72 20 62 65 20 6c  6f 61 64 65 64 20 69 6e  |her be loaded in|
00000190  74 6f 20 53 69 64 65 77  61 79 73 20 52 41 4d 20  |to Sideways RAM |
000001a0  6f 72 20 62 6c 6f 77 6e  20 6f 6e 74 6f 20 61 6e  |or blown onto an|
000001b0  20 45 50 52 4f 4d 2e 0d  54 68 65 20 63 6f 64 65  | EPROM..The code|
000001c0  20 68 61 73 20 62 65 65  6e 20 64 65 73 69 67 6e  | has been design|
000001d0  65 64 20 6e 6f 74 20 66  6f 72 20 63 6f 6d 70 61  |ed not for compa|
000001e0  63 74 6e 65 73 73 20 6f  72 20 6f 70 74 69 6d 69  |ctness or optimi|
000001f0  73 61 74 69 6f 6e 2c 20  62 75 74 20 74 6f 0d 61  |sation, but to.a|
00000200  6c 6c 6f 77 20 65 61 73  79 20 69 6d 70 6c 61 6e  |llow easy implan|
00000210  74 61 74 69 6f 6e 20 6f  66 20 65 78 74 72 61 20  |tation of extra |
00000220  63 6f 6d 6d 61 6e 64 73  20 61 6e 64 20 72 65 61  |commands and rea|
00000230  64 61 62 69 6c 69 74 79  2e 20 28 57 68 65 6e 20  |dability. (When |
00000240  49 20 66 69 72 73 74 0d  73 74 61 72 74 65 64 20  |I first.started |
00000250  77 72 69 74 69 6e 67 20  52 4f 4d 73 2c 20 49 20  |writing ROMs, I |
00000260  75 73 65 64 20 74 6f 20  77 72 69 74 65 20 63 75  |used to write cu|
00000270  73 74 6f 6d 20 68 65 61  64 65 72 73 2c 20 77 68  |stom headers, wh|
00000280  69 63 68 20 61 6c 77 61  79 73 20 6d 61 64 65 0d  |ich always made.|
00000290  75 70 64 61 74 65 73 20  64 69 66 66 69 63 75 6c  |updates difficul|
000002a0  74 20 74 6f 20 69 6d 70  6c 65 6d 65 6e 74 20 61  |t to implement a|
000002b0  6e 64 20 65 72 72 6f 72  2d 70 72 6f 6e 65 2e 29  |nd error-prone.)|
000002c0  20 53 6f 6d 65 20 63 6f  64 65 72 73 20 77 69 6c  | Some coders wil|
000002d0  6c 20 6c 6f 6f 6b 20 0d  61 74 20 74 68 69 73 20  |l look .at this |
000002e0  63 6f 64 65 20 61 6e 64  20 66 72 6f 77 6e 20 61  |code and frown a|
000002f0  74 20 74 68 65 20 75 73  65 20 6f 66 20 77 68 61  |t the use of wha|
00000300  74 20 73 65 65 6d 73 20  6c 69 6b 65 20 75 6e 6e  |t seems like unn|
00000310  65 63 65 73 73 61 72 79  20 4a 4d 50 20 0d 69 6e  |ecessary JMP .in|
00000320  73 74 72 75 63 74 69 6f  6e 73 2e 20 48 6f 77 65  |structions. Howe|
00000330  76 65 72 2c 20 69 74 20  69 73 20 73 70 65 63 69  |ver, it is speci|
00000340  66 69 63 61 6c 6c 79 20  77 72 69 74 74 65 6e 20  |fically written |
00000350  69 6e 20 73 75 63 68 20  61 20 77 61 79 20 74 68  |in such a way th|
00000360  61 74 0d 65 61 63 68 20  63 6f 64 65 20 73 65 63  |at.each code sec|
00000370  74 69 6f 6e 20 69 73 20  74 6f 74 61 6c 6c 79 20  |tion is totally |
00000380  69 6e 64 65 70 65 6e 64  65 6e 74 20 6f 66 20 65  |independent of e|
00000390  61 63 68 20 6f 74 68 65  72 20 61 6e 64 20 74 68  |ach other and th|
000003a0  75 73 20 63 6f 64 65 20  61 6e 64 0d 64 61 74 61  |us code and.data|
000003b0  20 63 61 6e 20 62 65 20  69 6d 70 6c 61 6e 74 65  | can be implante|
000003c0  64 20 61 6e 79 77 68 65  72 65 20 77 69 74 68 6f  |d anywhere witho|
000003d0  75 74 20 61 6e 79 20 72  65 6c 61 74 69 76 65 73  |ut any relatives|
000003e0  20 6d 6f 76 69 6e 67 20  6f 75 74 20 6f 66 20 0d  | moving out of .|
000003f0  72 61 6e 67 65 2e 20 28  47 6f 6f 64 62 79 74 65  |range. (Goodbyte|
00000400  20 42 59 54 45 20 65 72  72 6f 72 73 21 29 0d 20  | BYTE errors!). |
00000410  20 20 41 64 76 61 6e 63  65 64 20 52 4f 4d 20 63  |  Advanced ROM c|
00000420  6f 64 65 72 73 20 73 68  6f 75 6c 64 20 6e 6f 74  |oders should not|
00000430  20 74 68 61 74 20 74 68  69 73 20 68 65 61 64 65  | that this heade|
00000440  72 20 65 78 61 6d 70 6c  65 20 64 6f 65 73 20 4e  |r example does N|
00000450  4f 54 20 0d 73 75 70 70  6f 72 74 20 41 75 74 6f  |OT .support Auto|
00000460  62 6f 6f 74 2c 20 50 72  69 76 61 74 65 20 57 6f  |boot, Private Wo|
00000470  72 6b 73 70 61 63 65 20  43 6c 61 69 6d 73 20 6f  |rkspace Claims o|
00000480  72 20 43 6c 61 69 6d 73  20 6f 66 20 74 68 65 20  |r Claims of the |
00000490  4e 4d 49 20 57 6f 72 6b  2d 0d 73 70 61 63 65 20  |NMI Work-.space |
000004a0  6f 72 20 7a 65 72 6f 2d  70 61 67 65 20 6c 6f 63  |or zero-page loc|
000004b0  61 74 69 6f 6e 73 2e 20  49 66 20 79 6f 75 20 72  |ations. If you r|
000004c0  65 71 75 69 72 65 20 74  68 65 73 65 20 73 65 72  |equire these ser|
000004d0  76 69 63 65 20 63 61 6c  6c 73 2c 20 79 6f 75 0d  |vice calls, you.|
000004e0  73 68 6f 75 6c 64 20 69  6d 70 6c 61 6e 74 2f 69  |should implant/i|
000004f0  6e 74 65 72 63 65 70 74  20 74 68 65 6d 20 69 6e  |ntercept them in|
00000500  20 74 68 65 20 53 65 72  76 69 63 65 20 45 6e 74  | the Service Ent|
00000510  72 79 20 70 61 72 74 20  6f 66 20 74 68 65 20 73  |ry part of the s|
00000520  6f 75 72 63 65 0d 63 6f  64 65 2e 20 28 4e 6f 74  |ource.code. (Not|
00000530  20 66 6f 72 67 65 74 74  69 6e 67 20 74 6f 20 61  | forgetting to a|
00000540  64 64 20 72 65 6c 65 61  73 65 20 63 6c 61 69 6d  |dd release claim|
00000550  73 20 61 6c 73 6f 21 21  21 29 0d 20 20 20 54 68  |s also!!!).   Th|
00000560  65 20 66 69 72 73 74 20  70 61 72 74 20 6f 66 20  |e first part of |
00000570  74 68 65 20 63 6f 64 65  20 63 6f 6e 73 69 73 74  |the code consist|
00000580  73 20 6f 66 20 61 20 73  74 61 6e 64 61 72 64 20  |s of a standard |
00000590  52 4f 4d 20 68 65 61 64  65 72 2c 20 61 73 20 75  |ROM header, as u|
000005a0  73 65 64 0d 62 79 20 61  6c 6c 20 50 61 67 65 64  |sed.by all Paged|
000005b0  20 52 4f 4d 73 2e 20 28  50 6c 65 61 73 65 20 6e  | ROMs. (Please n|
000005c0  6f 74 65 20 74 68 61 74  20 49 20 68 61 76 65 20  |ote that I have |
000005d0  72 65 6d 6f 76 65 64 20  74 68 65 20 62 75 67 20  |removed the bug |
000005e0  69 6e 20 74 68 65 20 0d  68 65 61 64 65 72 20 74  |in the .header t|
000005f0  68 61 74 20 74 68 65 20  41 63 6f 72 6e 20 45 6c  |hat the Acorn El|
00000600  65 63 74 72 6f 6e 20 41  64 76 61 6e 63 65 64 20  |ectron Advanced |
00000610  55 73 65 72 20 47 75 69  64 65 20 63 6f 6e 74 61  |User Guide conta|
00000620  69 6e 73 21 21 29 20 54  68 65 20 52 4f 4d 0d 74  |ins!!) The ROM.t|
00000630  69 74 6c 65 20 69 6e 20  74 68 69 73 20 68 65 61  |itle in this hea|
00000640  64 65 72 20 69 73 20 74  68 65 20 74 65 78 74 20  |der is the text |
00000650  74 68 61 74 20 69 73 20  75 73 65 64 20 74 6f 20  |that is used to |
00000660  63 6f 6d 70 61 72 65 20  61 67 61 69 6e 73 74 20  |compare against |
00000670  61 6e 64 0d 70 72 69 6e  74 65 72 20 77 68 65 6e  |and.printer when|
00000680  20 61 20 2a 48 45 4c 50  20 63 6f 6d 6d 61 6e 64  | a *HELP command|
00000690  20 69 73 20 72 65 63 65  69 76 65 64 2e 20 48 6f  | is received. Ho|
000006a0  77 65 76 65 72 2c 20 61  6c 74 65 72 69 6e 67 20  |wever, altering |
000006b0  74 68 69 73 20 73 6f 20  74 68 61 74 0d 61 6e 6f  |this so that.ano|
000006c0  74 68 65 72 20 74 65 78  74 20 73 74 72 69 6e 67  |ther text string|
000006d0  20 69 73 20 75 73 65 64  2c 20 69 73 20 76 65 72  | is used, is ver|
000006e0  79 20 65 61 73 79 20 61  6e 64 20 6f 6e 6c 79 20  |y easy and only |
000006f0  72 65 71 75 69 72 65 73  20 63 68 61 6e 67 69 6e  |requires changin|
00000700  67 20 6f 6e 65 0d 45 51  55 57 20 73 74 61 74 65  |g one.EQUW state|
00000710  6d 65 6e 74 2e 20 41 20  70 6f 72 74 69 6f 6e 20  |ment. A portion |
00000720  6f 66 20 74 68 69 73 20  74 65 78 74 20 69 73 20  |of this text is |
00000730  61 6c 73 6f 20 70 72 69  6e 74 65 64 20 62 79 20  |also printed by |
00000740  74 68 65 20 6f 70 65 72  61 74 69 6e 67 0d 73 79  |the operating.sy|
00000750  73 74 65 6d 20 77 68 65  6e 20 61 20 2a 52 4f 4d  |stem when a *ROM|
00000760  53 20 63 6f 6d 6d 61 6e  64 20 69 73 20 69 73 73  |S command is iss|
00000770  75 65 64 2e 0d 20 20 20  54 68 65 20 43 6f 6d 6d  |ued..   The Comm|
00000780  61 6e 64 20 44 61 74 61  20 69 73 2c 20 61 73 20  |and Data is, as |
00000790  69 74 73 20 6e 61 6d 65  20 73 75 67 67 65 73 74  |its name suggest|
000007a0  73 2c 20 74 68 65 20 63  6f 6d 6d 61 6e 64 73 20  |s, the commands |
000007b0  74 68 61 74 20 61 72 65  0d 61 63 63 65 70 74 65  |that are.accepte|
000007c0  64 20 62 79 20 74 68 65  20 53 65 72 76 69 63 65  |d by the Service|
000007d0  20 52 4f 4d 2e 20 41 6c  6c 20 6f 66 20 74 68 69  | ROM. All of thi|
000007e0  73 20 74 65 78 74 20 62  65 74 77 65 65 6e 20 74  |s text between t|
000007f0  68 65 20 6c 61 62 65 6c  73 20 2e 63 64 74 20 0d  |he labels .cdt .|
00000800  61 6e 64 20 2e 63 64 65  20 69 73 20 70 72 69 6e  |and .cde is prin|
00000810  74 65 64 20 62 79 20 74  68 65 20 52 4f 4e 20 77  |ted by the RON w|
00000820  68 65 6e 20 61 20 2a 48  45 4c 50 20 63 6f 6d 6d  |hen a *HELP comm|
00000830  61 6e 64 20 69 73 20 72  65 63 65 69 76 65 64 20  |and is received |
00000840  77 69 74 68 20 61 6e 0d  61 72 67 75 6d 65 6e 74  |with an.argument|
00000850  20 6f 66 20 74 68 65 20  52 4f 4d 20 74 69 74 6c  | of the ROM titl|
00000860  65 2e 20 2a 48 45 4c 50  20 77 69 74 68 20 6e 6f  |e. *HELP with no|
00000870  20 61 72 67 75 6d 65 6e  74 73 20 6a 75 73 74 20  | arguments just |
00000880  79 69 65 6c 64 73 20 74  68 65 20 52 4f 4d 0d 74  |yields the ROM.t|
00000890  69 74 6c 65 73 20 61 6e  64 20 76 65 72 73 69 6f  |itles and versio|
000008a0  6e 20 6e 75 6d 62 65 72  2e 20 45 61 63 68 20 52  |n number. Each R|
000008b0  4f 4d 20 63 6f 6d 6d 61  6e 64 20 69 6e 20 74 68  |OM command in th|
000008c0  69 73 20 64 61 74 61 20  62 6c 6f 63 6b 20 73 68  |is data block sh|
000008d0  6f 75 6c 64 0d 68 61 76  65 20 69 74 73 20 6f 77  |ould.have its ow|
000008e0  6e 20 6c 61 62 65 6c 20  61 6e 64 20 62 65 20 74  |n label and be t|
000008f0  65 72 6d 69 6e 61 74 65  64 20 77 69 74 68 20 63  |erminated with c|
00000900  61 72 72 69 61 67 65 20  72 65 74 75 72 6e 20 28  |arriage return (|
00000910  26 30 44 29 20 66 6f 72  20 0d 72 65 61 64 61 62  |&0D) for .readab|
00000920  69 6c 69 74 79 27 73 20  73 61 6b 65 20 77 68 65  |ility's sake whe|
00000930  6e 20 65 63 68 6f 65 64  20 74 6f 20 74 68 65 20  |n echoed to the |
00000940  73 63 72 65 65 6e 2e 20  50 6c 65 61 73 65 20 62  |screen. Please b|
00000950  65 20 61 77 61 72 65 20  74 68 61 74 0d 6c 6f 77  |e aware that.low|
00000960  65 72 63 61 73 65 20 74  6f 20 75 70 70 65 72 63  |ercase to upperc|
00000970  61 73 65 20 63 68 61 72  61 63 74 65 72 20 63 6f  |ase character co|
00000980  6e 76 65 72 73 69 6f 6e  20 69 73 20 75 73 65 64  |nversion is used|
00000990  20 69 6e 20 74 68 65 20  63 6f 6d 70 61 72 69 6e  | in the comparin|
000009a0  67 20 6f 66 0d 69 73 73  75 65 64 20 63 6f 6d 6d  |g of.issued comm|
000009b0  61 6e 64 73 20 28 75 6e  72 65 63 6f 67 6e 69 73  |ands (unrecognis|
000009c0  65 64 20 63 6f 6d 6d 61  6e 64 73 20 74 68 61 74  |ed commands that|
000009d0  20 61 72 65 20 6f 66 66  65 72 65 64 20 74 6f 20  | are offered to |
000009e0  74 68 65 20 50 61 67 65  64 0d 52 4f 4d 73 29 20  |the Paged.ROMs) |
000009f0  73 6f 20 70 6c 65 61 73  65 20 64 6f 20 6e 6f 74  |so please do not|
00000a00  20 75 73 65 64 20 77 65  69 72 64 20 63 68 61 72  | used weird char|
00000a10  61 63 74 65 72 73 20 6f  72 20 6e 75 6d 62 65 72  |acters or number|
00000a20  73 20 69 6e 20 79 6f 75  72 20 63 6f 6d 6d 61 6e  |s in your comman|
00000a30  64 0d 6e 61 6d 65 73 2e  20 53 68 6f 75 6c 64 20  |d.names. Should |
00000a40  79 6f 75 20 64 65 73 70  65 72 61 74 65 6c 79 20  |you desperately |
00000a50  72 65 71 75 69 72 65 20  6e 75 6d 62 65 72 73 20  |require numbers |
00000a60  69 6e 20 63 6f 6d 6d 61  6e 64 20 6e 61 6d 65 73  |in command names|
00000a70  2c 20 79 6f 75 20 77 69  6c 6c 0d 6e 65 65 64 20  |, you will.need |
00000a80  74 6f 20 72 65 71 72 69  74 65 20 74 68 65 20 43  |to reqrite the C|
00000a90  6f 6d 6d 61 6e 64 20 49  6e 74 65 72 70 72 65 74  |ommand Interpret|
00000aa0  65 72 20 28 61 6e 64 20  70 6f 73 73 69 62 6c 79  |er (and possibly|
00000ab0  20 74 68 65 20 48 65 6c  70 20 49 6e 74 65 72 2d  | the Help Inter-|
00000ac0  0d 70 72 65 74 65 72 20  61 6c 73 6f 29 2e 0d 20  |.preter also).. |
00000ad0  20 20 54 68 65 20 53 65  72 76 69 63 65 20 45 6e  |  The Service En|
00000ae0  74 72 79 20 69 73 20 74  68 65 20 70 69 65 63 65  |try is the piece|
00000af0  20 6f 66 20 63 6f 64 65  20 63 61 6c 6c 65 64 20  | of code called |
00000b00  77 68 65 6e 20 74 68 65  20 52 4f 4d 20 69 73 20  |when the ROM is |
00000b10  65 6e 74 65 72 65 64 0d  61 6e 64 20 74 68 65 72  |entered.and ther|
00000b20  65 20 69 73 20 6e 6f 74  68 69 6e 67 20 63 6f 6d  |e is nothing com|
00000b30  70 6c 65 78 20 61 62 6f  75 74 20 74 68 69 73 20  |plex about this |
00000b40  63 6f 64 65 2e 20 49 74  20 73 69 6d 70 6c 79 20  |code. It simply |
00000b50  73 74 6f 72 65 73 20 74  68 65 20 52 4f 4d 0d 65  |stores the ROM.e|
00000b60  6e 74 72 79 20 72 65 67  69 73 74 65 72 73 20 61  |ntry registers a|
00000b70  6e 64 20 72 65 73 74 6f  72 65 73 20 74 68 65 6d  |nd restores them|
00000b80  20 6f 6e 20 65 78 69 74  2e 20 54 68 65 20 63 6f  | on exit. The co|
00000b90  64 65 20 6f 6e 6c 79 20  73 75 70 70 6f 72 74 73  |de only supports|
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00001ad0  74 79 2e 6e 65 74 0d                              |ty.net.|
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