Tristar & Red Sector Inc.
present
< -- --- A M S T A I R --- -- >
[ AMSTrad Antic Internal Ripper ]
version : 1.1
released on : April 2025 @ Revision
designed by : Raft^TRSi
THE AMSTAIR TOOL
A bit of context
As far as I remember I always wanted to have a led display of the Amstrad CPC signals, like on the old skool Altair / Imsai / educational kits... you know, Xmas tree vibes!
But obviously these LEDs would blink too fast to see anything. The CPC had to be slowed down. Since the Wait signal is used by the Gatearray, I had to find another way. The DMA mode was my second choice, although I often read that it was difficult to use on CPC...
As things advanced I really had fun with DMA and it appeared that this little project finally had some usefulness !
So I decided to design a tool based on my experiments, with these guidelines in mind:
* The gear should look Ooold SKooooool
* No CPU, only LOGIC components of the CPC era (also because I had quite a lot of these TTL LS chips in my drawers)
* Have fun!
Tool Features
Beyond its Educational interest, AMSTair offers you a way to Hack your games in real time, Debug code / ports, Diagnostic faulty CPC and much more...
* Display CPC control lines via LEDs
* Slow down your Amstrad at chosen speed
* Freeze mode with step by step functionality : Step on each Clock, DMA access, CPU instruction, port read, port write, Memory access
* Select the IO port you want to scan
* Show address lines in binary and data lines in hexadecimal
* Output the selected data to SOUND (Really?!)
* Digiblaster compatible mode
* DMA read or write in each cpu modes : fast, slow, paused
* DMA can r/w Memory and IO ports
* Selection of DMA address and data via switchs
* Selection of Port or Memory address to intercept via switchs
* Force DMA for dead z80
* CPC or external power supply
* Reset Amstrad
This tool is compatible with the Amstrad CPC 464, 646, 6128, 464 Plus and 6128 Plus
Video Presentation
AMSTAIR [ AMSTrad Antic Internal Ripper ] - CPC Tool / TRSi
Amstair technical ressources : Files / Schematics
Here you can get the fabrication files (Gerber, components list...)
Disclaimers
This is a home made personal project. TRSi and the designer of this tool can not be held responsible for any physical or psychological damages or consequences that could occur with this tool. If you decide to get one, or build one, it's at your own risk!
And of course, unplug it when not in use.
Want a PCB/kit ?
If you don't want to bother making a PCB I may launch a new batch in the future. I can provide the PCB only, or a kit with the components. But I probably won't provide a soldered product, and even less a cased one ;)
I am still not sure of the cost yet. Probably around 40-50Euros for the kit.
Contact me if you are interested at raft.gm(at)gmail.com !
HOW TO USE IT
AMSTAIR User Manual - Quickstart Guide
1. CPU MODE
- Normal : No DMA. Z80 runs at normal speed
- Fast : DMA activated. Z80 at 99.9% speed. DMA is set to minimize its impact on the CPC internal timings (ex: Disc drive can operate in this mode)
- Slow : DMA activated. Control the speed of your CPC with the appropriate potentiometer (13)
- Paused : DMA activated. CPU is freezed until you press the STEP button (12). Steps types are determined by the VIEW MODE
2. VIEW MODE
The Address Leds Bars and Data Hexadecimal views are updated depending on the following selection
- CLK : Live display
- OPCODE : Display Z80 instruction code
- DMA : Display DMA reads (16 bits selection with switch 4)
- IO IN : Display PORT INPUT access (8 highest bits selection with switch 4)
- IO OUT : Display PORT OUTPUT access (8 highest bits selection with switch 4)
- MEMORY : Display RAM/ROM Memory access (8 highest bits selection with switch 4)
Note : The selected mode is defining the STEP style
Note2: When in IO/MEMORY scan mode, remember to select the opposite DMA (with switch 6). Otherwise you will intercepct your own DMA calls ;)
3. Sound ON/OFF
Output the current DATA displayed to the speaker of the CPC
4. Address switchs to select
- 16 bits DMA address to read or write
- 8 high bits of the RAM/ROM adress when in "MEMORY" VIEW MODE
- 8 high bits of the PORT when in "IO IN" or "IO OUT" VIEW MODE
5. Data switchs to select
- 8 bits to send/write with DMA
6. RAM / IO switch
Select between RAM/ROM or IO DMA mode
7. DMA Write
Send the selected DATA to the selected RAM Address or PORT
8. CPC control signals
Show the activity of the CPC (unlatched).
Note : The active-low signals are inverted
9. BUSAK
The Blue LED displays the DMA activity
WARNING : The switch is used to force DMA and should only be used on a CPC with a removed/dead Z80!
10. Reset
Reset the CPC
Note : Usefull when you set the tool to "Paused" CPU MODE
11. Power Ext/CPC
CPC : The Amstrad power supply is used to power AMSTAIR
EXT : Use of an additionnal 5V power supply
Note : Recommanded to use an external PS, even more if other interfaces are connected
OLDSKOOL is PAINFULL POWERFULL