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YABUS.IDE8255

An IDE multiplexer based on 8255 PIO. It's construction is very simple, however reading in MODE 1 givies 19T Z80 per byte.

The 8255 is seen in ports #1B, #3B, #5B, #7B and only one logic chip is behind 8255 outputs. Also, the 8255 inside MB-02 can be used with special cable (no changes inside required).

Disk protector

If the power supply for disk is separated from power supply for IDE8255, the /ATCS0, /ATCS1, /ATRD and /ATWR lines behave as being in low state, when the IDE8255 is off. This can result in buring the disk. (We buried this way the CL-SH260-15QC-D chip of Seagate ST351A/X.)

To prevent such situation, the /ATCS0 should not be connected directly to GND, but with transistor (as OC with +5V on base). The /ATCS1 instead of being connected directly to +5V, should be separated with 1N4148 diode. The changes are not required, when there is only one power switch for both IDE8255 and disk.

Amstrad CPC version

A special version of IDE8255 was prepared for Amstrad CPC. The 8255 is seen in following ports:

PA#F8E6, #FAE6, #FCE6, #FEE6
PB#F9E6, #FBE6, #FDE6, #FFE6
PC#F8E7, #FAE7, #FCE7, #FEE7
RS#F9E7, #FBE7, #FDE7, #FFE7

As while reading data the PA and PB are read periodicly, eight INI comannecs can be used in a row, reading following ports: #F8E6, #F9E6, #FAE6, #FBE6, #FCE6, #FDE6, #FEE6, #FFE6. Of course this can be done only with e.g. #F8E6 and #F9E6, but this requires more frequent reloading of B register (of Z80CPU).


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Files for download

ide8255-003.zip 44.0kB (2004-02-13 17:07)
Board v003, Eagle data files.
ide8255.txt 4.5kB (2003-09-18 15:19)
[en] The idea of fast IDE multiplexer based on 8255.

Links to other pages



See also

PL3MEM - ZX Spectrum IDE (ATA)
External box for ZX Spectrum with 128kB EPROM, 32kB SRAM in ZX+3 switching and 16b IDE interface.
YABUS.ZX
Two YABUS slots for ZX Spectrum computers.
YABUS.TF3
4MB RAM extension for Timex FDD 3 with YABUS support.
DSKHNDLR
Low level floppy and hard disk drivers for Z80.
PPI 8255 parallel interface
Most popular parallel interfaces based on 8255 PPI. Hardware type, port addresses, slot type, description of options.

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© 2009-12-28 21:50 Jarek Adamski, http://8bit.yarek.pl