Aspect

ASPECT

Editor/Assembler

Bug-Byte Software





INSTRUCTIONS FOR ASPECT



The program "ASPECT 4.2", its documentation and artwork are

strictly the copyright of Bug-Byte. It is illegal to make a

copy of ASPECT 4.2 without authorisation from Bug-Byte and legal

action will he taken against anyone found doing so.





Introduction



Aspect 4.2 is a combined Editor Assembler designed to aid the

production of machine code programs and subroutines

on the Sinclair Spectrum Computer.. Aspect 4.2 does not affect the

stack pointer and temporary storage used by the

Spectrum Basic Language ROM. This is a deliberate part of the

design of Aspect as it is assumed that many programmers

would wish to use Aspect to design machine code subroutines as

"add-ons" to the existing BASIC language commands. This

also allows the use of the Spectrum tape system for loading and

saving both source code and object code.





Getting Started



If you do not already possess one, it is advisable to obtain a

copy of PROGRAMMING THE Z80 by Rodnay Zaks, or a similar Z80 tutor and

reference book.

To run Aspect 4.2, enter:

LOAD ""

The first program to load is the Aspect basic bootstrap loader

"aspload" which will execute automatically, load Aspect 4.2,

clear the screen and then jump to execute it.



The Commands



Upon execution of Aspect 4.2 the commands available are as follows:-

A = Assemble program Ln = goto text line number n

B = Backup through text one line N = clear text buffer for NEW program

Dn = Delete next n lines of text R = Return to Spectrum BASIC

E = Edit current line S = Show symbol table after assembly

Fn = Forward through next n lines Vn = View next n lines of text

H = Hunt for line or string Wn = Show WHERE text buffer starts and

I = Insert text before current line ends



To enter a command just type the command letter followed by the

parameter 'n' if needed.





Using the Editor



The Keyboard



The first difference that you will notice between Aspect 4.2 and

Spectrum BASIC is that the keyboard loses all of its

normal multi-shifted functions. It will now perform as as ordinary

alphanumeric teletype-like keyboard - the only difference

is the function of the DELETE key - this has now been changed so

that you have to push SYMBOL SHIFT instead of CAPS

SHIFT to obtain the delete function. This was done so that it is

possible to delete characters with a one-handed action.



The only characters that will now work under Aspect 4.2 are those

that are necessary to the editing and assembly of

programs. You cannot for instance use coloured text or user-defined

graphics as entries to the editor, although these

facilities of the Spectrum will still work if called from your

own machine code programs.





User Input Errors



If you make on error in the entry of a command then Aspect 4.2

will reply with the question mark [?] symbol and prompt

you to enter a further command character.





Editor Commands



Insert ... The Insert command has two functions: the first is to

allow the entry of text into on empty buffer; the second is to

allow text to be inserted into the buffer at any position in the

source code listing. This command always inserts text before

the current line.



Delete ... The Delete command allows the user to delete either

the current line or the next n consecutive lines of text.

(NB. Use this command carefully.)



List ... This command allows the current location of the editing

pointer to be altered and thus determines from which line

of text all other commands perform their action.

To look at a particular line of text in the buffer, type the

command [Ln] where n equals the number of the particular line

within the buffer; to go to the top of the buffer type [L].



View ... To look at a number of consecutive lines in the buffer

type [Vn] where n equals the number of lines to scroll

through. (16 is a good choice - ie. [V16] - the editor will then

display the next 16 lines of text in the buffer.



Backup ... This command allows the user to move the current

editing pointer back through the text file; ie. to back up 5

lines type [B5].



Forward ... The Forward command allows the user to move the current

editing pointer forward through the text.



Hunt ... The Hunt command tells the editor to search for the given text

string and set the current line number to the location of the occurrence

of that string; eg- HLABEL will hunt for the word LABEL.



Edit ... If a line has to be edited, the user first of all sets the

current editing pointer to the line with the L command and then types E.

The editor then prints the line on the screen and places the cursor at

the end of it. The user may then backspace along the line to change the text.



Where ... This command shows the user where the start of text, and the

end of text, and memory limit are. The output is in hexadecimal numbers.



New ... This command enables the user to clear the text buffer and resets

the editing pointer to the top of the buffer.



Return ... The Return command enables the user to return intact to the

Spectrum BASIC Interpreter. To get back to Aspect 4.2 from BASIC enter:

PRINT USR 24576

This will warm start the editor and your text should still be intact.



Assemble ... When the source program text has been entered correctly and

checked for errors, the procedure to assemble is to type the letter [A]

and hit Return. The user will see the source and object listing appear on

the Spectrum screen. If the program is quite large the listing can be

stopped for examination by depressing any key and continued by depressing

any key. Once the listing reaches the end of the program it will type the

letters EOF on the screen; the object code is then in memory starting at

the LOAD address.



Show ... This command enables the user to print on the screen a cross

reference table for all the labels in the assembly.





Aspect 4.2 Syntax



The syntax of the source program should be as that of the Zilog Z80

Assembly Language Programming Manual; ie-

Label: Operator Operand; Comment

START: LD HL,MSG1; this is a comment

MSG1: DB "this is a message"; this is another comment

The label should always be separated from the operator by a colon, the

operator from the operand by a space and the comment should always be

separated from the code by a semi-colon.

Hex digits are allowed and are specified by adding an H after the number.

Enter it as 0FFFFH.

The symbol $ can be used to represent the program counter for relative

jumps, etc. For example the jumps in the following program are all allowed.

All are assembled as jumps back to the program start.



ORG 7800H JP $-3

LOAD 7800H JP START

START: JP 7800H END



Pseudo-ops. The following operators are not part of the Zilog Z80

instruction set but are understood by Aspect 4.2. They should be used in

exactly the same way as normal operators.

ORG. Program origination address; eg- [ORG 08000H]. This statement sets

the origin point for the program counter to work from. It may be used any

number of times in the code to organise the program for different addresses.

LOAD. Object code output start address; eg- [LOAD 07800H]. It is possible

to set ORG and LOAD for different addresses in cases where the memory the

program will finally run in is not available during assembly.

You MUST include both an ORG and a LOAD pseudo-op at the start of

every program; eg

ORG 7800H

LOAD 7800H

This will assemble the code at address 7800 hex.

EQU. Used to assign a symbol to a variable; eg- [SCREEN: EQU 4000H]

DS. This tells the assembler that the next X locations must be allocated

as defined storage space. The define space command needs to be put on a

line on its own; eg- to define an area 100 bytes long, labelled DATA, use:

DATA:

DS 100

- do not enter it as:

DATA: DS 100

DW. This generates a word or two bytes in the object file in reversed

order as required by the 16-bit instructions of the Z80.

DB. This operator causes all the bytes on the same line to be inserted in

the output code in order; eg- [MSG1: DB 20H,24H,23H] or [MSG1: DB "this

is Aspect 4.2"].

END. It is essential to terminate the assembly source code with an END

statement otherwise the assembler will give an EOF error.



Aspect 4.2 Memory Allocation

Aspect 4.2 automatically sets itself up for the correct memory size and

resides at location 24576 (decimal) or 6000 (hex). It is approximately 4K

long and the text buffer start and end location can be obtained by using

the W command, which will give the start of buffer, end of buffer and top

of memory. There is a space of approximately 450 bytes between the end of

the assembler and the text buffer for the symbol table. All of Aspect's

storage and stacks are kept inside the 4K allocated to it. It is not wise

to load code below about 7800H as this will affect the operation of the

Sinclair BASIC.



Cassette Operations

Both source code and object code can be saved and loaded by using the

Sinclair Basic Tape Operating System with the commands as follows:-

[LOAD "filename" CODE (start address),(length)]

[SAVE "filename" CODE (start address),(length)]

The correct syntax and use of these commands can be found in chapter 26

in the ZX Spectrum manual.

When saving listings, use the W (Where) command to find the end of the text

buffer and then SAVE the CODE from the start of Aspect (24576) to the end

of the text buffer. To reload, simply use:

LOAD "" CODE

- and PRINT USR 24576 after loading for a normal re-entry from BASIC. There

is no need to load in Aspect first.





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of BOOTS and W.H. SMITHS, or in our advertising in the computer press and

elsewhere.



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a copy on cassette to:

THE PROGRAMMING DEPARTMENT, BUG-BYTE, 100 THE ALBANY, OLD HALL STREET,

LIVERPOOL L3 9EP

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program to our range. Or simply send an S.A.E. for details of our terms

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