Hi Jo Even!

on Thu 10-08-2000 21:37 Jo Even Skarstein wrote:
>
>I vaguely recall that you use a Stacy/MSTE SCSI-card in your Mega.

That is correct, although that particular MST is now standing unused.
(I've got another one with 36MHz accelerator and IDE interface now.)


>I have a spare card myself, and I'm planning on installing it in my
>sister's boyfriend's Mega. However, I can't find the pinout on the card's
>ACSI connector. I believe I have the pinout for the Mega's connector, but
>it has fewer pins so I assume they're different.

They are very different, as illustrated further below.


>Do you have, or know where I can find, this pinout?

I have it, measured by myself as I haven't found it elsewhere.

 Stacy/MSTe ACSI I/F
----------------------
 1:OD0          2:HD0
 3:OD1          4:HD1
 5:OD2          6:HD2
 7:OD3          8:HD3
 9:OD4         10:HD4
11:OD5         12:HD5
13:OD6         14:HD6
15:OD7         16:HD7
17:HDReset     18:HDAck
19:HDCS        20:HDA0
21:HDRW        22:HDReq
23:XHDInt      24:nc
25:Gnd         26:Vcc+
27:Gnd         28:Vcc+
29:Gnd         30:Vcc+
----------------------

In the above OD0..OD7 are the buffered outputs intended to drive the next
ACSI unit, while HD0..HD7 are the unbuffered inputs to be connected to the
Mega ST DMA expander (the 24 pin connector), described below.

 Mega ST DMA expander
----------------------
 1:Gnd          2:HD0
 3:HDReset      4:HD1
 5:Gnd          6:HD2
 7:Gnd          8:HD3
 9:Gnd         10:HD4
11:HDAck       12:HD5
13:Gnd         14:HD6
15:Gnd         16:HD7
17:Gnd         18:HDCS
19:HDA0        20:Gnd
21:Gnd         22:HDRW
23:HDReq       24:XHDInt
----------------------

Since the even-numbered pins in range 2..16 of both connectors are for
the same signals on both connectors it is easiest to base the adaptor
on keeping those leads to minimum length.


Additional ACSI units may be connected either to a new 19-pin connector
using OD0..OD7 from the Stacy/MSTe interface for the data lines, or to
the existing 19-pin connector of the Mega ST.  There are some drawbacks
of both methods, however.

Using OD0..OD7 increases the buffer delay to external ACSI units, which
may be critical if several are connected in series.

Using the normal ACSI connecter for external ACSI units may cause overload
of the HD0..HD7 outputs from the Mega ST motherboard.

On the other hand, I have myself used both methods successfully !


Btw: If you can find a schematic for the ACSI-SCSI interface of Atari's
Megafile 44 (the Syquest unit), this gives a very good idea of how the
STacy/MSTe interface works.  They are chip-for-chip identical, although
some of the details of pin usage differ (eg: reversed buffer bit order).

I myself used this as an aid in modifying my interface, in three ways:

1:  Parity generator (simple, single chip add-on)
2:  Second drive select (simple, using free on-board gates)
3:  CDROM compatibility (complex, needs PCB cutting and new chips)
    (Compatibility was extended to 7-bit commands, but not 8-bit.)


>Thanks in advance,

It is always a pleasure to help another Atarian.

-- 
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Regards:  Ronald Andersson                  mailto:dlanor@ettnet.se
http://dlanor.atari.org/    ICQ:38857203    http://www.ettnet.se/~dlanor/
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