Conference hydra::amiga_v1

    re: critical length
    
    keep it as short as possible. i.e, solder the 86 pin connector to a
    board and mount the adaptor chips on this board. solder the 62 pin
    connector to this board and connect the xt controller.
    
    the signals should not travel more than 3 inches to get to the OMTI.
    
    now, if you buffer every signal coming in or out of the
    adaptor/controller via 74LS245's, then you can mount the controller up
    to about 18 inches away. I know a guy who built this up with buffers
    and the basic formatter ran, but the system wouldnt access the drive.
    
    HIS CABLE WAS ABOUT 2 FT LONG!!!!!! when he shortened it, it worked.
    
    hope this helps
    
    Glenn.

    Thanks Glenn, It does help. I'm not surprised by the answer, but it is
    good to hear the voice of experience confirm my suspicions.
    
    It does raise some other questions though. If I decide to buffer the
    bus with 74LS245's what signals beside R/W determine bus direction?
    
    What signals, if any, should be used as tri-state enable/disable?
    
    By inference, it is not critical where the OMTI (ST11-M in my case)
    sits in RElation to the disk drives. Is this correct?
    
    On a design point; I was unable to obtain 74HC688 Magnitude Comparator,
    but was able to get a 74LS684.  My thinking is to use one of the
    redundant gates in the 74LS32 and OR the -AS signal with the (-P=Q)
    output from pin 19 of the comparator. This should be funtionally
    identical to the 74HC688. Have I got it Right?  I will have an extra
    gate delay, but is this critical?
    
    Lastly is the 86pin edge connector 2 X 43 way at 0.1 pitch? If so I
    may have found a UK supplier.
    
    		Thanks again for your help
    				Best Regards,
    					David
    

    re:.2
    
    David,
    
    	I've uploaded to TAPE::USER2:[UPLOADS] AN UPDATED CIRCUIT FOR THE
    CHEAPHD/MAKEHD PROJECT. 
    
    Look for SUPER_CHEAPHD.LZH
    
    This has buffering on the expansion bus and some status LEDS. It has
    been built...and works. (check the pin-outs on the 245's - I am told
    (but have not confirmed) that there is an error.
    
    The interface between the XT controller and the Drive is via
    differential drivers. I remember reading that this allows a cable
    length of six metres. Mine worked quite OK with 3 metres of cable.
    
    The connector is a 2 by 43 connector with 0.1 inch pitch.
    
    Hope that this helps.
    Cheers
    Glenn.

    Glenn,
    	Many thanks for the help. I will certainly take a look at SUPER_HD
    circuit.  Though with possibility of 3 m of cable from the ST-11
    contoller, I can afford to position the adaptor right next to the
    Amiga.
	Once I have verified the UK supplier I will post the details here
    for other builders in the UK.
    
    	I'm working now on a sutable PCB layout and finding it tedious. To
    many connections at opposite ends of the board and too many conflicting
    and crossing tracks.  Is there any PD PCB design software around?
    
    Thanks again, I'll let you know how it goes.
    
    					Regards,
    						David
    

    Are you putting the Amiga board in this box also ?
    
    	Is this cable screened ?
    
    Mine is built as described earlier , with short distance between each
    edge connector.
    
    			-Pete-

    Pete,
    	I had not considered putting the Amiga motherboard into the PC350
    box until I saw your earlier note.  I'll consider it.   I've yet to do 
    any of the real practical work as I'm still trying to get hold of an 86
    pin connector.  I've identified one manufactured by MOWLEX but they are
    having to send to the USA for a sample. They've agreed to send one to
    me as soon as they recieve it.
    
    	I have downloaded the SUPER_CHEAPHD circuit from TAPE which buffers
    the bus using 74LS245's. this permits a bus extension of about 1 ft.
    Which is about as much as I need if I keep the Amiga and expansion box
    seaparate. No mention is made of cable screening so I was planning on
    using flat ribbon cable.
    
    			Regards,
    				David
    

    The S100 Bus used to be popular ,
    
    Try getting a 100 way connector and cut it down !!!
    
    	Mine was found in the shed , so I cannot recommend a supplier.
    Probably came from a scrap machine at some time.. Try going to
    a breakers  Don't always buy new.
    
    		.Pete.

    Pete,
    	Good Idea. It had ocurred to me to do the same, just hadn't got
    round to it. No news from MOWLEX. The samples from them would be FREE,
    but how long can I wait?????
    
    			Regards,
    				David
    

    Yippee!!!! MOLEX cam across with the goods this morning.
    Part No. 87087-0043.  They are PCB mounting types, so will need some
    work to fit a straight A500.  Mine were FREE samples but should be
    available through Electronic retailers or agents.
    
    MOLEX inc.      			Telephone: 312/969-4550
    2222 Wellington Court
    Lisle                               Telex:    20-6070/25-4069
    Illinois 60532
    USA
    
				   Regards
    					David.
    

    My ST-11-M controller came without any physical detail on it's
    numbering of pinouts.  It looks to be numbered from left to right
    irrspective of which side of the board you are looking at eg:
    
    !------------------------------!  !------------------------------!
    !				   !  !                              !
    !				   !  !                              !
    !				   !  !                              !
    !     COMPONENT SIDE  "A"	   !  !      ETCH SIDE  "B"          !
    !				   !  !                              !
    !				   !  !                              !
    !				   !  !                              !
    !				   !  !                              !
    !				   !  !                              !
    !UUUUUUUUUUUUUUUUUUUUUUUUUUUUUU!  !UUUUUUUUUUUUUUUUUUUUUUUUUUUUUU!
     1                            31   1                            31
    
    Is this correct?
    
    Secondly how is the A 500 expansion port numbered. My manual just gives
    a list of pins and no physical layout?
    
    Any help wil be greatly appreciated. I've no wish to fry anything by
    connecting either of these 180 degrees out.
    
			Regards
    				David
    

    re .10
    Further to my question about the expansion port. There is a schematic
    in the manual showing the pins to be numbered on alternate sides but
    which is pin 1?  Upper left?
    
    			Regards,
    				David
    

Hi

	ST11-M   ..Why ? It's MFM  .

	I thought you had an RD53 ? The price is the same for ST11-R and
you get 33Mbyte more data area on the disk !

	Anyway I had this problem, The way I satisfied myself was to meter
the 5v from the 74 series chip to the edge connector and via the drawings
to the Amiga !

	If you take the top off the Amiga Pin 1 is marked.

	As for the ST11-M if it the same as the ST11-R I'll have to check mine
out.



			-Pete-

Who is in Highfield week starting the 10th of December

    Pete,
    	I went for an ST-11M for safety being unsure whether operating RD53
    in RLL was really reliable. I also have and RD51 which I will us as
    drive 2.
    
    	Thanks for the tips. I guess I'll get the meter out. I was just
    being lazy really.
    
    	I might pop into Highfield next week for a chat.
    
    				Regards,
    					David