Z80 Assembly programming for the Elan Enterprise 128

What is the Enterprise 128?
The Enterprise 128 is an 8 bit Z80 system, it's comparable to the Amstrad CPC,however it has more advanced Memory Mapping which allows more flexible bank switching, and more advanced graphics

Like the CPC screen it can function at 320x200 at 4 colors, and you can halve the resolution to get 160x200 with 16 colors... unlike the CPC, there is a 256 color mode of 80x200
All these modes can be 'half resolution' of 100 vertical pixels

The Enterprise doesn't just have more colors though! compared to the CPC, a screen that can be split into sections, and each section can be a different screen mode and color pallete - this can be done with clever interrupts on the CPC, but the Enterprise does this in hardware, without interrupts or cpu power used - allowing for far more colorsplits, The color palette is also better - the regular CPC has 27 possible colors, but the Enterprise has 256

The Basic Enterprise has 64k, but we'll be focusing on the 256k version

Cpu 4 mhz Z80
Ram 64k / 128k
Resolution 320x200 4 color
160x200 16 color
80x200 256 color
Sound chip 3 Channel sound (non AY)

Useful Documents


ChibiAkumas Tutorials

Lesson H5 - Hello World on the Elan Enterprise

Lesson S3 - Easy Sprites on the Enterprise
    Lesson P1 - Basic Firmware Text functions

Lesson P2 - More Text Functions, Improvements... and the Sam Coupe!

Lesson P3 - Bitmap graphics on the Amstrad CPC and Enterprise 128

Lesson P7 - Keyreading on the MSX, Enterprise and TI-83

Lesson P14 - Palette definitions on the Enterprise and Sam Coupe

Lesson P19 - Sound on the Elan Enterprise

Lesson P27 - Bankswitching and hardware detection on the Enterprise

Lesson P38 - Playing Digital Sound with WAV on the Sega MasterSystem/GameGear, Elan Enterprise and GameBoy/GBC

Memory Banks

The Enterprise and it's OS supports up to 256x 16k banks for an insane 4MB of memory (though some may be rom!)
The most basic system supports 64k, but there is also a 128k version (the EP128)...
There are two special segments... the Zero Segment containing the RST's, and our program, (loaded at &0000) and the system segment (loaded at &8000 by default)... around 2/3rds of the system bank will be used by the OS... the rest will be free.

it's important to notice, ONLY memory banks in the base 64k (&FC FD FE FF) can be used for video memory.
We can use the Zero page bank if we want... but we must 'request' ALL other banks from the OS before using them... it will find one, and tell us what it's allocated - if all the banks are used, it will give us the spare memory of the system page,

The diagram to the right, shows how the OS allocates memory on these two systems.
Essentially the internal memory has bank numbers 255-252 (FF-FC)... as we add more memory, we will get lower and lower numbered banks... for example a 256k system will have banks down to 240 (F0)

The top bank (255) is used as the system segment... the bottom bank (number will depend on upgrades) will be the Zero page...

The system will allocate banks in consecutive order... so we won't use the internal 64k until we have no choice... this means we can be sure to have it available for Vram!

Low numbers (for example banks 0-4) will be rom.

Bank switching is performed by simply writing the bank number (Eg &FC) to the ports &BO &B1 &B2 and &B3 with an OUT command
64k System   128k System
FC (Zero) F8 (Zero)
FF (Sys) FB

FF (Sys)
64k Bank (Can be Vram)
Extended bank (Cannot be vram)

Banks witching Ports:

 Address  Port
&0000 &B0
&4000 &B1
&8000 &B2
&C000 &B3

Asking for memory... and giving it back to the OS!
We can ask the OS for memory, and then use it for whatever we want... if we don't need it any more, we can tell the OS to take it back!

This is how we get a free VRAM bank... we ask for memory banks, until we get one >=FC (a 64k internal bank)... This may take a while, as the OS gives us the low numbered banks first... but once we get one, we can just free up all the ones we didn't really want!

We use RST 6 to do an EXOS call... and command 24 to request a segment, and 25 to give it back!

Lets look at the details of these two commands:

EXOS Function 24 - Allocate Segment
This command will request another 16k segment...  status reg will be Zero if succeeded, NZ if another full 16k is not available
If succeeded the segment number will be returned in C... if only a shared segment was available, the boundary will be in DE
Parameters:    none
Returns:  A=status    C=segment number    DE=EXOS boundary within this segment (if returned is a shared segment, otherwise &4000)

EXOS Function 25 - Free Segment
This command will free a 16K segment of RAM. The segment must have been allocated via EXOS function 24.
Parameters:  C=segment number
Returns:  A=status       

If we don't need the OS, we can just use the memory ourselves without asking...
But if we want it to do Disk reading or other things for us, we need to play nice!
It all depends on how you plan to use the system, and how worried you are about compatibility.

Screen Memory

The Enterprise screen memory location and layout is defined by a LPT block
Each Line contains 16 bytes in the format below:

Offset Name Bytes Example
0 SC 1 256-200 LLLLLLLL Two's complement of the number of scanlines in this mode line. Zero means 256 scanlines.
1 MB 1 %01010010 ICCRMMML I   VINT=0, no IRQ
CC  Colour Mode=01, 4 colours mode (2/4/16/256)
R   VRES=1, full vertical resolution (full/half)
MMM Video Mode=001, pixel graphics mode
L   Reload=0, LPT will continue
2 LM 1 11 SSLLLLL S    Special bits in 2 color mode
L    Left Margin
3 RM 1 51 SSRRRRR S    Special bits in 2 color mode
R    Right Margin
4 VIDADDR 2 &0000 LLLLLLL HHHHHHHH Memory address of Vram in first 64k of memory (low number banks - not 128k upgrade)
6 VIDADDR2 2 ? LLLLLLL HHHHHHHH Second Video Data address - not used in pixel graphics Modes
8 COL0-7 1x8 %00000111 g0  r0  b0  g1  r1  b1  g2  r2 8 palette definitions (8-15 are the same, with FIXBIAS offset)
16 SC - - - Next line in the LPT block 


Reading from the keyboard on the enterprise is easy.
There are 10 rows, from 0-9, we just send the number of the row we want to port &B5, we then read in from port &B5 to get the status of the keys in that row.

Reading the Joystick in is also done from port &B5 , however to select the row we use port &B6.

IN &B5 IN &B6
bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0 bit 2 bit 1 bit 0
0 LShift Z X V C B \ N J1-F3 J1-F2 J1-F1
1 Ctrl A S F D G Lock H

2 Tab W E T R Y Q U

3 Esc 2 3 5 4 6 L 7

4 F1 F2 F7 F5 F6 F3 F8 F4

Erase ~ 0 - 9
8 J2-F3 J2-F2 J2-F1
] : L ; K

7 ALT Enter Left Hold Up Right Down Stop

8 INS Space Rshift . / , Delete M


[ P @ O


General Ports on the Enterprise (&80-&83=NICK)

Port Purpose Bits Bit Meaning
&80 Fixbias (Color 8-15 top bits) %----GRBGR Top 5 bits of color 8-16
(bottom BGR bits are 000,001,010 etc up to 111)
&81 Border Color
Eight bit colour value which will be displayed outside the margins of all mode lines.(%GRBGRBGR)  ;g0 | r0 | b0 | g1 | r1 | b1 | g2 | r2 | - x0 = lsb
&82 LPL � Line Paramater Table Low Byte Low part (A4..A11) of the line parameter base pointer.(%AAAAAAAA) A=Address bits 11-4
&83 LPH � Line Paramater Table High Byte High part of the line parameter base pointer.(%LC--AAAA) A=Address bits 15-12 , L=Load base C=Clock in line
&B0 Ram page 0 (0000-4000)

&B1 Ram page 1 (4000-8000)

&B2 Ram page 2 (8000-C000)

&B3 Ram page 3 (C000-FFFF)

&B4 Interrupt latches

&B5 Select keyboard/joy row (out)

&B5 read keyboard row (in)

&B6 Read Joy row (in)

&B7 WR2 / RD2 (in/out)

&BF Ram options (out) (&0C = fast)

Sound ports on the Enterprise (DAVE)

Port Purpose Bits Bit Meaning
&A0 Channel 0 Tone L LLLLLLLL L=Tone Low Byte� Lower values=Higher tone
&A1 Channel 0 Tone H RPCCHHHH H=Tone High Bits / polynomial Counter / Ring Modulator (CH2) / highPass Filter (CH1)
&A2 Channel 1 Tone L LLLLLLLL L=Tone Low Byte� Lower values=Higher tone
&A3 Channel 1 Tone H RPCCHHHH H=Tone High Bits / polynomial Counter / Ring Modulator (CHN) / highPass Filter (CH2)
&A4 Channel 2 Tone L LLLLLLLL L=Tone Low Byte� Lower values=Higher tone
&A5 Channel 2 Tone H RPCCHHHH H=Tone High Bits / polynomial Counter / Ring Modulator (CH0) / highPass Filter (CHN)
&A6 Noise Channel frequency RHLBCCNN Noise (0=31khz 1-3=Channel 0-2 link) / polynominal Counter/ swap Bits 7 & 17 of pc / Lowpass /Highpass / Ring modulator
&A7 Sync & Interrupt rate -IIDDSSS Interrupts (0=1khz,1=50hz,2=tone0,3=tone1) D=D/A ladder on (speccy 48k emu) / Sync for tone 0,1,2 (1=hold 0=run)
&A8 Tone Channel 0 LH Amplitude --VVVVVV V=Volume(63=max)  
    D/A ladder (If &A7 Bit3=1... tape port, Speaker L)
&A9 Tone Channel 1 LH Amplitude --VVVVVV V=Volume(63=max)  
&AA Tone Channel 2 LH Amplitude --VVVVVV V=Volume(63=max)  
&AB Noise Channel LH Amplitude --VVVVVV V=Volume(63=max)  
&AC Tone Channel 0 RH Amplitude --VVVVVV V=Volume(63=max)  
    D/A ladder  (If &A7 Bit4=1... tape port, Speaker R)
&AD Tone Channel 1 RH Amplitude --VVVVVV V=Volume(63=max)  
&AE Tone Channel 2 RH Amplitude --VVVVVV V=Volume(63=max)  
&AF Noise Channel RH Amplitude --VVVVVV V=Volume(63=max)  

EXOS (RST 6 / RST 6*8) functions

Meaning IN Param A IN Params (other) OUT Result A 
Out Params (other)
0 System Reset
C=Reset type flags Status
1 Open Channel Channel Number
2 Create Channel Channel Number
3 Close Channel Channel Number
4 Destroy Channel Channel Number
5 Read Character Channel Number
Status B=Character
6 Read Block Channel Number BC=Byte Count DE=Buffer Address Status BC=Bytes left to read DE=Modified buffer address
7 Write Character Channel Number B=Character Status
8 Write Block Channel Number BC=Byte Count DE=Buffer Address Status BC=Bytes left to write DE=Modified buffer address
9 Channel Read Status Channel Number
Status C=Status (0=Ready -1=EOF 01=otherwise)
10 Set and Read channel status Channel Number C=Write Flags DE=Parameter block Status C=Read Flags
11 Special Function Channel Number B=Subfunction Number C+DE=Unspecified Status C+DE=Unspecified




16 Read,Write or Toggle EXOS variable
B=Action (0=Read 1=Write 2=Toggle)
C=ExosVar number D=NewValue
Status D=New value
17 Capture Channel Main Channel number C=Secondary channel number Status
18 Redirect Channel Main Channel number C=Secondary channel number Status
19 Set default device name
DE=Device name pointer C=Device type Status
20 Return System Status
DE=Parameter block Status B=Version number
21 Link Device
DE=Pointer to Device descriptor BC=Ram Required Status
22 Read EXOS Boundary

Status C=Shared Seg number DE=EXOS boundary in seg
23 Set User Boundary
DE=Offset of user boundary in seg Status
24 Allocate segment

Status C=Segment number DE=EXOS boundary in seg
25 Free segment
C=Segment Status
26 Scan System extensions
DE=Pointer to command string Status
27 Allocate channel buffer
DE=Amount of buffer in one seg BC=amount of buffer which can be in multiple segs Status IX=Allocated bufer Page1=New buffer seg
28 Explain Error code Error Code DE=String buffer 0
29 Load Module
DE=Buffer B=Channel to load from Status B=1st char / Module type / undefined
30 Load relocatable module
B=Channel number DE=Starting address to load at Status
31 Set time
C=HH D=MM E=SS (BCD) Status
32 Read Time

Status C=HH D=MM E=SS (BCD)
33 Set Date
C=YY D=MM E=DD (BCD) Status
34 Read Date

Status C=YY D=MM E=DD (BCD)

For full details See page 50: EXOS20_technical_information.pdf

EXOS Variables

Use with EXOS call 16 (set C to var number)

Name Description
3 DEF_TYPE Type of default Device (0=NonFile 1=File)
4 DEF_CHAN Default channel number (used when 255 specified)
5 TIMER 1hz
6 LOCK_KEY Keyboard lock status
7 CLICK_Key 0=enabled
8 STOP_IRQ 0=Stop causes IRQ >0=Stop returns code
9 KEY_IRQ 0=Any key causes soft IRQ
10 RATE_KEY in 1/50 of a second
11 DELAY_KEY 0=no autorepeat
12 TAPE_SND 0=Sound enabled
13 WAIT_SND 0=sound driver waits when queue full
14 MUTE_SND 0=Speaker enabled >0=Speaker disabled
15 BUF_SND Sound envelope storage in phases
16 BAUD_SER Baud serial rate
17 FORM_SER Serial word format
18 ADDR_NET Network address of machine
19 NET_IRQ 0=Data received causes IRQ
20 CHAN_NET Channel number of net block received
21 MACH_NET Source machine of network block
22 MODE_VID Video Mode (On page open)
23 COLR_VID Color Mode (On page open)
24 X_SIZ_VID X page size (On page open)
25 Y_SIZ_VID Y page size (On page open)
26 ST_Flag 0=Status line displayed
27 BORD_VID Border color (%GRBGRBGR)
28 BIAS_VID Color Bias for palette colors 8-16 (%----GRBGR)
29 VID_EDIT Channel number of video page for editor
30 KEY_EDIT Channel number of Ketboard for editor
31 BUF_EDIT Size of edit buffer (in 256 byte pages)
32 FLG_EDIT Flags to control reading from editor
33 SP_TAPE >0=Slow tape save
34 PROTECT >0=Write protected file
35 LV_TAPE Tape output level
36 REM1 State of Tape remote controls (0=on >0=off)
37 REM2 State of Tape remote controls (0=on >0=off)

Enterprise Programming Tutorials:

P3 - Bitmap graphics on the Amstrad CPC and Enterprise 128
P7 - Keyreading on the MSX, Enterprise and TI-83

General Z80 Assembly Tutorials:

B. Beginner series - Learn the basics
A. Advanced series - In more detail
M. Multiplatform series - programming methods that work on all systems

EP128emu - Enterprise Emulator - Set up guide
ep128.hu - great english enterprise 128 site
gafz enterprise forever site - another great english site
English Books for the EP128
Enterprise OS HTML documentation

Hello World

Here's my Hello World example. I couldn't find one, so I had to write it! It uses the operating system to access the screen and keyboard. This code was tested using WinApe - which is a CPC emulator, but it can compile ASM program code just fine
Download this from the sourcecode link at the top of this page!

write "..\RelEnt\program.com"

;            Hello World
;    Show a hello world message, then read a key
;    From the keyboard and show it.
;    Screen and keyboard ops use Enterprise OS calls
;    by opening 'stream' devices to the Keyboard and
;    screen

ORG &00F0
    DB0,5               ;type 5 - Binary Program
    DW FileEnd-FileStart       ;File length
    DB 0,0,0,0,0,0,0,0,0,0,0,0 ;Spacer
; org &0100
    LD SP,&100    ;set the Stack to a safe place

    ld c,MODE_VID        ;Set text mode
    ld d,0
    call ENT_Writevar

    ld c,COLR_VID        ;Set 2 color
    ld d,0
    call ENT_Writevar

    ld c,X_SIZ_VID        ; 40 Chars Wide
    ld d,40
    call ENT_Writevar

    ld c,Y_SIZ_VID        ;24 chars tall
    ld d,24
    call ENT_Writevar

    ld de,ENT_Screenname     ;Open Screen as stream 10
    ld a,10
    call ENT_OpenStream    

    ;Display the just opened screen
    ld a,10    ; A channel number (1..255)
    ld b,1    ; B @@DISP (=1) (special function code)
    ld c,1    ; C 1st row in page to display (1..size)
    ld d,24  ; D number of rows to display (1..27)
    ld e,1  ; E row on screen where first row should appear (1..27)
    call ENT_SpecialFunc

    ld de,ENT_Keboardname    ; Open the keyboard as stream 11
    ld a,11
    call ENT_OpenStream
;            INIT Done
    ld hl,Message
    call PrintString    ;Print Hello world message

    call NewLine        

    call WaitChar        ;Wait for a keypress

    push af
        ld hl,Message2    ;Print 'You Pressed' message
        call PrintString
    pop af
    call PrintChar        ;print the char the user pressed
    call NewLine

    halt    ;stop execution - I've not figured out how to return to basic!

Message: db 'Hello World!',255
Message2: db 'Key Pressed:',255

    ld a,(hl)
    cp 255
    ret z
    inc hl
    call PrintChar
jr PrintString

;        Functions for controling EXOS

MODE_VID  equ 22    ;Enterprise OS variable numbers
COLR_VID  equ 23
X_SIZ_VID equ 24
Y_SIZ_VID equ 25    

    ;Open stream A from device string DE
    ;DE should point to a string like...  db 6,'VIDEO;'  or db 9,'KEYBOARD;' (replace ; with a colon)
    rst 6
    db 1     ;open stream
    push de
    push hl
    push bc
        ld a,11
        rst 6
        db 5     ;read from channel - result in b
        ld a,b
    pop bc
    pop hl
    pop de
    push de
    push hl
    push bc
        ld b,a
        ld a,10
        rst 6
        db 7     ;write to channel a
    pop bc
    pop hl
    pop de

    ld a,13
    call PrintChar
    ld a,10
    call PrintChar
ENT_readvar:        ;readvar C from enterprise OS
    ld b,0
    rst 6
    db 16

ENT_Writevar:        ;WriteVar C=D to Enterprise OS
    ld b,1
    rst 6
    db 16

ENT_SpecialFunc:    ;Special Function (for displaying screen)
    rst 6
    db 11
;Device names db [length],'name;'
ENT_Screenname: db 6,'VIDEO:'
ENT_Keboardname: db 9,'KEYBOARD:'

Starting the program:

The program will show hello world, then pause for a keypress


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on Amazon in Print or Kindle!

Buy my Assembly programming book

Available worldwide!
Search 'ChibiAkumas' on
your local Amazon website!
Click here for more info!

Buy my Assembly programming book
on Amazon in Print or Kindle!

Buy my Assembly programming book

Available worldwide!
Search 'ChibiAkumas' on
your local Amazon website!
Click here for more info!