[sebhc] H-8-IDE board
West, Ronald S.
RONALD.S.WEST at saic.com
Thu Jul 22 09:13:34 CDT 2004
Finally got the hardware design for the H-8-IDE board completed. I am going
to start bread boarding the design (hopefully this weekend). I will find out
in short order any shortcomings in it soon as I get the breadboard done.
Thought I might make the schematic available on the SEBHC website for anyone
else who wanted to play around with this but cannot get my schematic capture
program to save in any other but native format. I think I can print it out
(B size paper) and then scan it in and create a gif file that way. Will work
on that and post it soon as possible.
The IDE board is hard wired on base address 200Q and uses all 8 address from
200Q to 207Q. The upper data byte register is at address 2100. These
addresses are in reserved I/O space just above the primary H17 device
addresses. I found a port assignments chart in appendix 1-C of the HDOS 3.0
system configuration book on the SEBHC website.
Soon as I get it built will write a small program to write test data to the
drive. After verifying the board works (reliably), will write a device
driver for it. If all goes well the drive should be able to store 65535 x
512 = 33,553,920 or 33.5 mega-bytes. Due to the way HDOS 2.0 (don't know if
3.0 is different) allocates files it will only store 400 files per disk
(including system and directory files). The neat thing is we may be able to
create SY0 through SY9 (10) disks on one hard drive. That will make up for
the limited number of files. The device driver will do the mapping between
drives. Due to memory restrictions I think HDOS only allows 3 or 4 drives to
be mounted at any one time so some creative drive management may be in
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