Table of Contents
PRCC, a new ecosystem for 8-bit processors of 70's and 80's
Processor, RAM, CPLD, and Compact flash (PRCC) is a new concept in modular system for 8-bit (and some 16-bit) processors of 1970's and 1980's. The processor can be Z80, 8085, 6809, 6502, 68008, and other 5-volt, 8-bit processors or 16-bit processors with 8-bit bus. The processor shares the same hardware resources of CPLD, RAM, and CF disk. Other boards such as video display, sound, and discrete I/O can be added to the core PRCC system.
PRCC is a modular computer system consists of an expandable backplane, 100mm X 100mm, with seven female 2×25 connectors. Each module is 100mm X 50mm with a corresponding 2×25 male connector that plugs into the backplane. Table 1 shows the signal assignments of the backplane connectors.
Processor module is a 5Volt 8-bit processor with most of its signals connected to the 2×25 connector. The addresses, data, power, reset, clock signals are fixed, but the processor control signals vary depending on the processor in use. The programmable CPLD will accommodate the different processor control signals and drive the rest of the system appropriately.
CPLD modules is the heart of the PRCC. A minimum PRCC is consists of a CPLD module and a processor module. CPLD contains a simple bootstrap ROM, an internal serial port, and necessary decoding logic to interface to the specific processor and control the RAM and compact flash drive. The CPLD serves as the diagnostic module when bringing up a PRCC system initially.
RAM module is the only memory in the system; there is no corresponding ROM module. It is at least 128K bytes in size, but can be up to 1 megabytes. RAM is divided into multiple banks of 32K per bank for most 8-bit processors. For processors with larger than 64K memory space such as Z180, Z280, and 68008, the processor has direct control of the RAM's address lines.
CF module is possibly the simplest board on PRCC. It is basically two IDE44 connector with terminating resistors; one for compact flash interface and the other for disk-on-module interface. Since PRCC is a ROM-less system (other than a small ROM located on CPLD), the CF disk contains the system software to be loaded into RAM by the bootstrap ROM in CPLD.
Future modules may be multi-channel serial port, video display, sound card, discrete I/O, SPI/I2C/parallel ports and others.