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added 8x2 LCD for debugging
added USB/serial RS232 converter + USB socket
hitechworld.org/index.php?title=68008_PiKey
this is a 68008 based single board computer with PIC powered RAM bootloader. 128k RAM, 8 MHz 68008, PIC 18f4450.
68k 68000 Motorola Freescale CPU
new prototype design.
the 68008 only has 8 bit data bus so less signals are required, as well only one RAM chip.
and I had a new idea to reduce the I/O interface for the bootloader. no EPROM is used here, but a PIC microcontroller loads data into the RAM.
previously I had 16 bit data bits, plus two latches for the address bus.
Now I am only using one latch, and the lower 4 bits are also connected to PIC I/O. Means the latch only needs to be updated every 16 bytes.
The PIC can only access the lower 4 Kbyte of the RAM where previously I allowed 64 Kbyte range. But this is unneccessary complicated to wire! the 68008 can copy memory blocks to the upper RAM areas, I was thinking, then again the PIC can load more data into the shared area.
Also the PIC and 68008 can run at the same time. at 48 MHz, the PIC is much faster for bit manipulation, for instance driving LCDs. the 68008 is more comfortable when handling 16 bits and 32 bits including multiplication/division. But it is not very fast for these instructions, MUL can take upto 70 cycles, DIV can take upto 170 cycles. Even some addressing modes can take upto 40 cycles.
PIC 18F4450
128K static RAM
68008
1x 74hc573 latch
ycprojects.wordpress.com
pic.hitechworld.org
WIKI here
hitechworld.org/index.php?title=68008_PiKey
This page is user editable and I can accept ideas, comments, links and all the like.
Most 68k single board computers I saw on the net are very complicated:
- 20 to 30 ICs
- CPLD for address decoding
- PCB absolutely required even if they are initially based on wire prototype.
Most users can not reproduce wire prototypes which are so complex
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