This is an expansion for Amiga 500 and plus providing 2MB Fast SRAM and one IDE port. I believe the two things that the A500 lacks the most are probably a hard drive, and Fast RAM.
The RAM is configured by default as 2MB Fast autoconfig (in the 200000-9FFFFF space), and it can be turned into a 1.5MB (fast) RAM in ranger space (C00000-D7FFFF) together with 512KB MapROM. This mode is targeted for owners of plus or expanded rev8a who want to play old picky games from floppies. The modes and maprom can be configured by maintaining the reset from 3 to 10s or by using the provided Amiga software.
Facts about this project :
- It sits under the CPU : does not block access to the ROM and does not need a relocator.
- I wanted a mini-IDE port, this is the main reason why I started to create my own board.
- I thought that it would be neat to have some Fast RAM on the same 2-layers PCB, and I had a great SRAM chip for another project, PCMCIA-SRAM.
- The IDE port simulates the one from the A600 so it is bootable with appropriate Kickstarts. Like other IDE expansions, it requires two additional signals from the motherboard : INT2 and OVR.
- By default, the RAM stuff takes the place of the first expansion in the autoconfig chain. To use other autoconfig expansions, you need to configure the firmware with config_in/out pins to put it in your autoconfig chain ; these pins take the place of the secondary LED.
- Version 0.3 of the board adds a "clockport" to connect compatible expansions. Its "SPARE_CS" is at address D8xxxx. It is untested at the time of writing
Thanks Guys :
- mkl from http://www.mkl211015.altervista.org has created both IDE and RAM expansions, ide68k and ram68k, that sit under the 68000, and can be stacked. I thank him for publishing his schematic and code since it inspired this project, and the base of the IDE CPLD code is a verilog conversion I made from his abel of version 425.
- Sector101 shared an interesting experiment that proved it is somewhat simple to use SRAM as fast memory, and encouraged me to try adding it to this project : https://blog.sector101.co.uk/2019/07/20/amiga-500-2mb-handwired-fastram-expansion/ .
- Sukkopera shared the OpenAmiga500FastRamExpansion from which I used the autoconfig CPLD code in earlier versions : https://github.com/SukkoPera/OpenAmiga500FastRamExpansion/
- the software in this project is inspired by the MapROM tool shared by Paul RASPA (PR77) https://github.com/PR77/A600_ACCEL_RAM/tree/master/Software . This is the first C code I ever compiled for my Amiga, so I believe the MapROM function was achieved thanks to this working starting point !
This is a hobbyist project, it comes with no warranty and no support. Also remember that the Amiga machines are about 30 years old and may fail because of such hardware expansions.
I publish my work under the CC-BY-NC-SA license. The content of this repository is the result of weeks of work, requiring investment in tools, parts, prototypes, and risky tests on his own equipment. For this reason the author does not want third parties to sell products and keep all the profit, usually without even offering support to their customers. If you see people selling this without the consent of the author, don't buy from them.
If you find it useful and want to reward my hard work : I am always looking for Amiga/Amstrad CPC hardware to repair and hack, please contact me.
- 1x XC95144XL CPLD
- 1x CY62167ELL-45ZXI 5V SRAM (do not use 3.3V CY62167EV !). For 4MB you may also, with small changes in the CPLD code (addressing and autoconfig) :
- stack a second chip on the first one and connect its pin 12 to the pad nearby -god skills required-,
- use a CY62177ESL-55ZXI 5V SRAM instead (rare, expensive, not tested).
- 1x 3.3v LDO, either SPX3819M5-L-3-3 or XC6206P332MR
- 2x 1uF (or more) 0805 capacitors
- 5x 100nF 0805 capacitors
- 3x 10k 0805 resistors
- 2x 4k7 0805 resistors
- 1x BAT54A (or equivalent) diodes
- 64x rounded socket pins, for CPU pass-through connection. I use pins taken from a socket header.
- 1x 2x22 2.0mm pin header. Remove pin 20 which is IDE key.
- 2x wires for INT2 and OVR signals
- optional : 1x LED and resistor (330 ohm 0805 for example)
Components are SMD, and have thin pin pitch. You need to know what you are doing.
Check for shorts at least between 5V, 3.3V, and GND traces before applying power !
The programming port does not need to be soldered since it needs to be programmed just once : you can just hold it in place during the few seconds required for programming.
CPLD code is generated and built into xsvf using Xilinx ISE 14.7 IDE then iMPACT. There are configuration defines for RAM type and LED/config_pins selection, choose the ones you need. The "Process Properties" of the Fitting step are tweaked :
- -slew = Slow
- -power = Low
- -nogclkopt = Checked (by default)
- -nogsropt = Checked (by default)
- -unused = NOT Checked (by default), since pin 4 is used as pass-through
There are several methods to program the XC95144XL, I personally use xsvfduino. I advise you program it when unplugged from the motherboard, otherwise make sure to power it from the motherboard and not your programmer or it might burn trying to power the whole system.
- Remove the 68000 CPU from the motherboard
- Insert the CPU on the expansion. I personally upgraded to a 68010 to gain the quit key ability with WHDLoad
- Plug the expansion in the motherboard. Take care of Pin 1. Push it firmly so it does not pop out of the socket during use, but do not break the CPU socket.
- Connect INT2 and OVR headers to the motherboard
- On the v0.3 board, connect INT6 to use the clockport expansions that need it
- Turn on the Amiga
Maintaining the reset for a few seconds will allow you to :
- 3s : disable MapROM for the next reboot
- 6s : turn off MapROM
- 10s : toggle the ram mode
You may use the provided FLACOntrol software to control the board from your OS. It exists in several flavours, with classic or unix-like command line arguments, or silent with minimal text output.
It provides a MapROM function that writes a 256K or 512K ROM image to F80000-FFFFFF. It also communicates with this expansion using a control register byte at $00E9Cxxx :
- bit 7 indicates if MapROM is active, write 0 to disable it at next reboot ;
- bit 6 is the current ram mode, 0 for Fast autoconfig and 1 for Ranger MapROM ; write it to change mode at next reboot.
To activate Ranger RAM with MapROM ; this will take effect at next reboot :
FLACOntrol -1
To map the internal ROM (might speed up the system) :
FLACOntrol -i
Or a different ROM from file, 256K and 512K are supported :
FLACOntrol -f Files:path/kickstart-image-not-swapped-nor-split.rom
It will revert to the hardware ROM at next power cycle or with :
FLACOntrol -x
And revert to the full autoconfig RAM and reboot immediately to take effect :
FLACOntrol -0 -r
To use the MapROM function more extensively, you may compile the CPLD firmware to provide MapROM by default, then add the following line to your startup-sequence. The -r flag tells the software to reboot the system after the new ROM is loaded, then during next reboot the software will exit since MapROM is already active, and your system will finish to boot with the new ROM :
FLACOntrol -f Files:path/kickstart-image-not-swapped-nor-split.rom -r