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Zoom inside the ColdFire
By Vincent Rivière

picture ColdFire CPU inside a FireBee
As the name implies, the heart of the ACP computer is a ColdFire microprocessor. We have chosen the model MCF5474, which is the fastest one. The ColdFire processor family is designed and produced by Freescale Semiconductor, the subsidiary of Motorola on semiconductors. The ColdFire chip is not only a CPU (like the 680x0 family was), it is actually a microcontroller. A lot of useful additional controllers are built directly into the ColdFire chip. They are directly usable on our computer, providing a very high level of integration. This is why the ColdFire is the best choice for designing a modern Atari-compatible computer.

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ColdFire is a CPU with many controllers and interfaces


- CPU 266 MHz
The main component of the MCF5474 is a ColdFire V4e Core. It is very similar to the 680x0 CPU family, but not fully compatible. Basically, some complex or rarely used instructions and addressing modes have been removed. Thus the ColdFire CPU is more simple and cheaper than any 680x0 CPU, while being a lot faster. With an additional lightweight software layer, the ColdFire CPU can be made compatible with existing 680x0 programs.

- FPU
The Floating Point Unit is the mathematical coprocessor. When used, it provides a big speedup for programs using intensive math functions. The ColdFire FPU is similar to the 68881, but it has limitations in instruction set and addressing modes, like the CPU.

- MMU
The Memory Management Unit can be used to provide Virtual Memory or memory protection between the different processes running on an operating system.

- Cache 32 KB x 2
The ColdFire cache is divided into a 32 KB instruction cache and a 32 KB data cache. The usage of the caches improves greatly the speed of the CPU, by optimizing the accesses to the external memory.

- SRAM 32 KB
The Static RAM is a high speed memory embedded into the ColdFire. It is required for DMA transfers, but can also be used for any other purpose when high performance is required.

- EMAC unit
The Enhanced Multiply-Accumulate Unit is a DSP-like unit supporting integer and fixed-point operations. It can be used to speedup some specific process such as image compression.

- PCI controller
The PCI bus has become the standard for extension boards in desktop computers. The ColdFire has built-in support for controlling PCI devices. This allows the usage of the hundreds of PCI boards available on the market. Of course specific drivers will have to be developed for every PCI card.

- DDR-SDRAM controller
The ColdFire can work with external DDR-SDRAM, for excellent performance. The ACP board has 512 MB of DDR-SDRAM built-in.

- Interrupt controller
The built-in interrupt controller can be compared with the MFP 68901, but a lot more flexible and powerful. It can use up to 63 interrupt sources with a specific exception vector for each source.

- Timers
4 General Purpose Timers (GPT) and 2 Slice Timers (SLT) are available. They are comparable to the Timers A/B/C/D of the MFP 68901, but more configurable.

- High Speed RS-232 controller
The built-in Programmable Serial Controller (PSC) can be configured as a RS-232 interface for high-speed transfers, including at 115200 bps.

- Ethernet 10/100 controller
A standard Ethernet controller is built directly into the processor. This allows an instant connexion to the local network and Internet.

- BDM / JTAG interfaces
These debug interfaces can be used with hardware debuggers or external software for monitoring the CPU activity or flashing the EEPROMS.

As you have seen, the ColdFire MCF5474 chip contains an incredible list of useful components, and there are even more.
The full documentation is available on the Freescale website.
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