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|Written by Hans Summers|
|Tuesday, 26 January 2010 03:21|
NOTE: This page is for information only. It's been many years since anyone has been active on this group project.
These are my preliminary design notes for the prototype CPCNG computer. The official CPCNG website (http://cpcng.free.fr) no longer exists. It used to contain a complete description of what the CPCNG computer is, why we are building it, the operating system, the applications software and the current state of the project. The descriptions and diagrams on this page are intended as a basis for discussion and a guide for the developer of the FPGA which will form the backbone of the prototype. Additionally they will provide a precise specification of the prototype hardware, I/O map and memory map for the group developing the emulator.
Prototype Board Contents
The prototype board will contain the following components:
A simplified block diagram of the prototype is shown below. This shows the interconnection of the various units discussed below and it will be apparent that most of the units will be coded in the FPGA. This diagram does not show the control signals (WR/RD/IOREQ etc.) which would overcomplicate the diagram at this level.
We will use an eZ80 CPU. A supplier has been located (WBC Europe), who are willing to provide them in small quantities at a price of £9.93 each (approx USD 14, EUR 16, FRF 105, DEM 31). The eZ80 actually comes as the eZ80190 Webserver, which is an eZ80 core plus various on-chip timers and interfaces. This chip is now available (Oct-01) but since it is new there is a lead time of some 2 months according to WBC.
We will use PC-type SDRAM cards for the main memory. A 128K fast SRAM will also be used as video RAM and in the CPC compatibility mode. A 128K ROM (EPROM or EEPROM) will contain boot code and any other required code e.g. the old CPC ROM's for the compatibility mode. The eZ80 address space is 16M, and the large SDRAM will be mapped in up to 256 4M blocks giving a total capacity of up to 1G. The 128K video RAM and 128K ROM will be mapped at programmable locations. Click here for a detailed description of the memory mapping.
The CPCNG will have a CPC mode where it will be able to run CPC software without modification. Software which relies on precise timing (e.g. demos) may not work as expected since the eZ80 is much faster than the old Z80, and certain software emulation of CPC hardware will be required. I have designed a draft circuit diagram for the CPC I/O intercept unit, with a detailed description: Read more...
The CPCNG will initially use PC-compatible peripherals. These are readily available and cheap, or even free where they can be salvaged from surplus or salvaged obsolete PC's. The peripherals used will be:
The prototype PCB will be produced in a small quantity, perhaps by a supplier such as Express PCB. It will contain the eZ80, 128K ROM, 128K SRAM, FPGA and sockets for: modem, keyboard, IDE hard disk, mouse, VGA monitor, power supply, SDRAM (PC cards) and several expansion sockets for further developments.
A large Field Programmable Gate Array (FPGA) will be used to implement all of the logic in the CPCNG, including the video circuit, IDE hard drive interface, memory mapping and CPC compatibility unit. The availability of FPGA's is a major advantage to us as it allows the use of complex logic circuits while minimising the chipcount, thus making the computer cheap and easily constructed by the group members.
Future versions of the CPCNG will include an advanced graphics processor and sound capabilities. The prototype described here deliberately omits these in an effort to minimise complexity. We need a prototype which is simple enough to be achievable, yet capable of expansion and operating as a test bed for the future verions. It is anticipated that once the CPCNG prototype board is working, a number will be built by members of the group, and hardware development will then expand. Different groups will be able to work on different sections of the hardware for the next version.
|Last Updated on Tuesday, 26 January 2010 03:52|