Everything You Always Wanted To
But Were Too Polite To Ask
Amiga Technical References
Q: Which CIA is associated with the parallel port?
A: U350 is the parallel port CIA; the other CIA is U300.
Q: Can the surface-mount CIAs used in the A4000 (and A1200) be removed and replaced with sockets for easier replacement in the future?
A: [Courtesy of Dale Currie of AmiTrix]
"These sockets are sometimes called Ultra Low Profile SMT sockets for PLCC Packages. The ones we get are AUGAT PCS-SMU Series. I believe ASSMANN also make them now, called SMT-PLCC-sockets. There are probably others.
They are only about half the height of a normal PLCC socket, and have flat pins turned underneath with slots in the bottom of the socket all around the inside edge, such that the pins sit on the SMT pads and you can solder them through the slots in the bottom of the socket. Needless to say, it's a very delicate operation, requiring a good iron with a very fine tip, a steady hand, and quite often the assistance of a magnifying glass/lamp.
Getting the CIAs off intact in the first place is another story. That requires some rather expensive gear (we use a PACE station, $1500-2000 CAN with all the attachments), but does a nice job. The only other way destroys the existing chips by cutting their pins and removing them one by one after the chip body has been freed. I wouldn't recommend it, unless you're very experienced, it's quite easy to destroy a pad/trace by overheating."
Mr. Currie may be contacted at
5312 - 47 Street
Beaumont, Alberta, T4X 1H9
Phone or Fax: 1+ 403-929-8459
Email: firstname.lastname@example.org or email@example.com
Q: What type of memory does the A4000 use?
A: The A4000 comes with either 1M or 2M of Chip RAM, either in a single SIMM
or surface-mounted on the motherboard. There are four SIMM sockets for expansion
memory (Fast RAM). These sockets hold 72-pin ("PS/2") SIMMs, either 1M or 4M in
capacity, 80 ns or faster (that is, 70 ns or 60 ns). EDO SIMMs can be
used, but will not operate any faster than plain non-EDO memory. It is not
possible to mix 1M and 4M sizes. 8M or even 16M SIMMs can be used in place of
two or four 4M SIMMs (with the jumper set to the 4M size). To fit properly,
these SIMMs should be single-sided modules. The total motherboard Fast RAM limit
is 16M, regardless of SIMM combinations. (These specifications describe the
motherboard memory; expansion boards may use other types of memory.)
Q: Can the A4000 use 36-bit SIMMs, instead of 32-bit?
A: Yes. The extra parity bits are ignored.
Q: Which ROM goes where?
A: U175 is ROM 391513, and U176 is ROM 391514.
Q: How does the lock on the front panel work?
A: [Courtesy of Marcel DeVoe]
It's a lock for the keyboard and mouse, completely disables them when it's
locked. And when it's locked, it's shorted. But the computer will
still boot, it doesn't disable the hard drive.
Floppy Drive Questions
Q: Why does the floppy light flash every so often, even with no disk in the drive?
A: This is a result of the system polling the drive to see if a floppy has
Q: Why doesn't my second floppy drive work in high-density mode?
A: Check for the proper setting of jumper J351 (see Internals/Motherboard
Jumpers). See also Floppy Drive
Q: Will normal PC-type double-density (720K) 3.5-inch floppies work in the A4000?
A: Yes, but you may encounter a couple of problems. First, many PC-type
floppies are not jumpered to support a diskchange signal. Enabling this may be
as easy as moving a jumper, or it may require unsoldering, moving, and
resoldering a surface-mount part. Secondly, many of the PC-type floppy drives
connect the diskchange signal to pin 34 of the connector; however, the Amiga
expects this signal on pin 2. A re-routing of the conductors in the cable can
solve this, or you can use the DiskChange command to manually notify the system
of disk changes.
Q: Will normal PC-type high-density 3.5-inch floppies work in the A4000?
A: No. [The following text courtesy of Gene Heskett] A commodity PC drive runs at normal spindle speed for the drive, or 300 rpm. To move data in and out of it in high-density mode requires a 500 kilobaud data pump in the floppy path. The Amiga chips are only able to handle around 400 kilobauds. The Amiga actually runs its floppy data rate at the older double density standard of 250 kilobauds.
To do high density on the older drives, special drives were ordered by Commodore that could run a fairly stable spindle speed of 150 rpm. If you watch it, you'd swear the drive was going to stop, it's that slow. These are the high-density drives for an Amiga, and until the chips get a refresh for a higher data rate, are the only type of drives that can be used in high density mode on an Amiga.
[Editor's note: some people have managed to modify standard drives; however, all reports indicate that these perform unreliably at best.]
I might add that since these custom Amiga drives run at half speed, the read
signal from the head is only about one-fourth of what a standard drive has, and
they do require an electrically quiet environment for a usable error rate. There
are a couple of other problems with using the PC drives, too: lack of a ready
signal for the automatic diskchange detection being one of them, and the lack of
talkback identify to tell the Amiga what kind of a drive it is is another. Even
if you could diddle the spindle speed down to 150 RPM (as its digital, that's
doubtfull) to make a high-density drive out of it, you'd still have to have a
custom driver that puts twice as many sectors on a track. The Amiga would
otherwise only do the normal double density sectors/track, and simply fill the
remaining space up with "trailer" bytes till the next index pulse came by,
thereby wasting half the track. The Amiga defaults to double density if the
drive doesn't talk back.
IDE Hard Drive Questions
Q: Can the A4000 support two IDE hard drives?
A: Yes, since IDE supports a master/slave drive setup. Make sure the drive jumpers
are set properly for two drives. You might have problems with two different
brands of drives working together; this depends on the age and type of the
Q: Can the A4000 use IDE hard drives larger than 512M?
A: Yes. The supposed "limit" of 512M is a limitation of the BIOS in MS-DOS
machines, and the A4000 is not subject to this limit. The maximum current
supported partition size is 4G, and the maximum drive size is 4G. If you want to
fully use larger drives, you'll have to look into replacing the 3.1 FFS with an
alternate filesystem. There is a beta test version of a new FFS with
larger capacities on the Amiga International web page: http://www.amiga.de/files/index.html.
Q: Can "EIDE" or "Fast ATA" hard drives be used in the A4000?
A: Yes. These are just different names for revised versions of IDE, and
should work fine with the A4000's on-board IDE controller.
Q: Files larger than 128K seem to be corrupted when I save them to an IDE hard drive. What's going on?
A: This is due to a bug that is common on IDE drives. To fix it, set the
MaxTransfer field to 0x1fe00 for each partition on the drive. Contrary to the
common misunderstanding, MaxTransfer specifies the largest transfer
size. This will work around the bug, and shouldn't greatly affect
SCSI Hard Drive Questions
Q: Does the A4000 come with a SCSI or SCSI-2 hard drive controller?
A: No. The A4000T (tower) model did (and does) come with a built-in SCSI-2
controller, though. The A4091 and FastLane expansion boards are common Fast
SCSI-2 controllers for the A4000, and the A2091 is a
fairly common SCSI-1 controller.
Q: Why doesn't SCSI work on the A4000?
A: It does. But because of a bug in early versions of the Zorro-III DMA
controller (the "Buster" chip), DMA SCSI controllers didn't work properly. This
problem can be fixed (by replacing the early revision 9 Buster with a revision
11 version) or avoided altogether (by using a SCSI controller that doesn't use
the Zorro-III bus, like the one built into the Warp Engine
Q: I have lots of questions about SCSI. Where should I look for information?
A: The SCSI
Examples document describes all the basic information.
Q: Why does my hard drive "stutter" every fifteen minutes or so, without the drive light coming on?
A: The drive is performing thermal recalibrations ("t-cals") to make certain
that the heads remain centered over the tracks as the platters heat up. The
so-called "AV" drives spread out t-cals so this momentary interruption doesn't
occur during "live" video or sound recording or playback.
Q: What is the pin-out for a DB25 SCSI connector? What about the standard 50-pin SCSI header?
A: See the Drives/SCSI Pin-Outs
section for both.
Q: Will SCSI hard drives meant for the Mac work on an A4000?
A: Yes. The cable included with most external Mac hard drives is a
DB25-to-Centronics 50 adapter, and this will work on a SCSI controller with DB25
external SCSI port. Software is available for accessing an existing Mac
filesystem, so file interchange with a portable SCSI device is possible.
Q: Will an EIDE CD-ROM drive work with the A4000's IDE interface?
A: Yes. Amiga International has a beta release of a new version of the scsi.device driver that supports ATAPI drives at http://www.amiga.de/files/index.html, and there are several other drivers in the disk/misc and disk/cdrom sections of Aminet. Beware of pseudo-IDE CD-ROM drives, like the older Mitsumi, Panasonic, and Sony drives, which will not work unless you have a special interface board for them.