Cromemco DPU Board This was a unique board. It's the only case I know of a Z80 and
68000 CPU chip on the one S-100 board. It was an extremely useful and
powerful board. Today it is quite a rare board. It was used
primarily for Cromemco's "Cromex Operating System".
The Cromemco 68000 board family is comprised of the DPD Dual Processor Unit,
MCU Memory Control Unit, and 256MSU and 512HS0 Memory Storage Units.
Based on the Motorola MC68000 microprocessor chip, the
Cromemco DPU introduced 32-bit computing speed and power to the Cromemco
line of computers. The DPU is a Dual Processor Unit, also incorporated an
8-bit Z-80A microprocessor chip to ensure compatibility with existing
software. Microprocessor selection is under software control, allowing the
programmer to select the chip of choice for any particular application or
routine. An existing Z-80 program, for example, could be run on the DPU with
a subroutine or two rewritten in 68000 code to speed things up. Appendix A
of the manual (see below) contained a Z-80 Assembly language program which
demonstrated the use of software controlled microprocessor switching
techniques.
And what about that program which doesn't quite all fit in main memory? With
a 24-bit wide address bus, the MC68000 can address up to 16 Mbytes of
memory. This is not bank-selected memory. The MC68000 could directly address
16 megabytes of RAM.
The Cromemco HCU Memory Controller Unit acted as an interface between the
S-100/IEEE-696 bus and the Cromemco M bus which runs between the MCU and its
associated MSUs. A single MCU worked in conjunction with up to eight MSU
boards providing not only an interface, but an error detection, correction,
and logging system. The Cromemco 256MSO provided 128K 22-bit words, each of
which includes six bits for error detection and correction. The 512MSO
provided 256K 22-bit words. This scheme allowed all single-bit errors to be
corrected and logged. The Cromemco 68000 board family conforms to the
S-100/IEEE-696 bus standard.
The Cromemco rather short manual for this board can be obtained
here.
The schematic can be obtained
here.
