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THE DX20
--------

The DX20 is a device whose purpose is to allow the connection of
IBM compatable equipment with the RH20 channel of the KL processor.
The DX20 takes MASSBUSS commands from the KL, and translates them
into IBM style channel commands.  The DX20 contains a minicomputer
which is programmed for this function.  Notice that the TU70 style
tape drives are also controlled by a DX20.  The only difference
between these two DX20s is a switch which is set to a particular
value.  Since the two types of DX20 are set with different values, the
monitor and microcode loaders can distinguish between those DX20s which
control disks and those which control tapes.

The monitor tries to distinguish between the two kinds of DX20 in
reporting problems with them.  The tape version of the DX20 is referred
to as a "DX20A" and the RP20 version is referred to as "DX20B".  BUGCHKs
BUGINFs, and BUGHLTs related to the DX20s are generally of the two forms
DXAxxx and DXBxxx, so that tape problems can be distinguished from disk
problems.  Finally, the BUGCHK and BUGINF output generally mention either
PHYX2 or PHYP2.  PHYX2 is the module name of the TU70 driver, and PHYP2
is the module name of the RP20 driver.

The DX20 has no external controls which the operator can use, nor does
it have any indicators to judge whether or not it is running.  Only
the examination of the MASSBUSS registers for the DX20 can indicate if
the microcode is loaded and running.  The monitor checks the microcode for
validity when it is first coming up, and checks to see if the microcode
is still running whenever any operation is started for a drive.  Various
BUGCHKs will be output when the microcode is known to be bad, such as
DXBDMI (DX20 microcode is invalid), DXBDIE (DX20B microcode halted), and
DXBHLT (DX20B controller halted).  On seeing one of these errors, the
affected RP20 disks will be off-line until the microcode is reloaded.

The BOOT program automatically loads microcode for all DX20s on the
system whenever a monitor is manually loaded by the operator.  BOOT
loads both tape and disk DX20s, using the unit type to decide which
type of microcode to load.  The microcode is contained within the BOOT
program itself, so that BOOT does not need any data file to load the microcode.
For each DX20 which BOOT loads, a message is output to the CTY informing
the operator which channel and DX20 number is being loaded, and whether
or not the load was successful.   On a failure, BOOT types the good and
bad data, and field service should be called to examine the problem.
BOOT does not load any microcode on a reload or if a dump is being taken.

Once the system is up and running, the DX20 should be running properly
since BOOT had loaded it.  If the microcode becomes corrupted or halts
because of some problem, the operator will have to reload it manually.
The DX20LD program is used for this.  The program has various commands
to load microcode, verify microcode, and start and stop the DX20.
The program gets the microcode from a file which is is in a special
format.  The standard names for the microcode files are as follows:

	TU70:	DXMCA.ADX
	RP20:	DXMCE.ADX

The normal action when running DX20LD is simply to type in the name
of the microcode file, and DX20LD will look around for the proper
DX20 and will load and verify the microcode into that DX20.  The file
names above are known to DX20LD, and specify as a default which kind
of DX20 to look for.  (Actually, any filename which starts with those
first five letters will work.  So that DXMCE-OLD.ADX would be
recognized as RP20 microcode, for example, but OLD-DXMCE.ADX would not).

If there is confusion between types of DX20 being loaded, the switches
/T (for TU70) and /R (for RP20) can be used to force DX20LD to load
only that type of DX20.  The switches will override the file names above,
so that a command like "DXMCE.ADX/T" will indeed load the disk microcode
into the wrong kind of DX20.

If there is not a unique DX20 to be loaded, you must specify the channel
and DX20 number of the DX20 you wish to load.  The /D:mn switch does
this, where "m" is the channel number, and "n" is the DX20 number.
For most systems, where there are at most one DX20 for tapes and one
DX20 for disks, the switch isn't necessary.  But if there were two DX20s
for disks for example, the /D switch has to be used to select
which DX20 to use.

DX20LD checks the microcode for validity after it loads it, and if
there are problems with the DX20 will complain about mismatches and
will type out good and bad data just like BOOT.  If this occurs,
field service should be called in to fix the problem.

Each RH20 on the system can handle up to eight DX20s, of any kind.
However, DX20s should "stick together".  That is, you should not
put a tape DX20 and disk DX20 on the same channel (even though it
might work).  It is also a bad idea to put RP06s or TM02s on the same
channel as a DX20.  However, it is just fine to put 8 disk DX20s on
the same channel (but expect this to be slow!!)

The 8000 controller
-----------------

The 8000 controller is a IBM-compatible disk controller which handles
up to 16 RP20 disks in dual ported mode, and 8 disks in single ported mode.
It is talked to by the DX20.  Only one 8000 controller can be controlled
by a DX20.  The 8000 controller is also a mini-computer, and it has its own
microcode distinct from the DX20 microcode.  It gets its microcode from
a floppy disk which should always be mounted in its floppy drive inside
the cabinet.  The microcode is loaded automatically when the 8000 is
powered on, when a power fail occurs, or when explicitly commanded by
using the maintainence switches inside the cabinet.  The KL processor cannot
read or write the microcode of the 8000, or start or stop it.  Therefore
the 8000 controller will in general require very little attention by the
operator since reloads, DX20LD, etc cannot affect it.

There is only one panel outside the cabinet which contains switches
and lights.  These are the port enabling switches for the 8000, labeled
"CHANNEL ENABLED" (A, B, C, and D) and "TAGGED".  In order for the 8000 to
control any disks, the "TAGGED" switch must be on (it lights up when it is
on) and the proper "CHANNEL ENABLED" switches must be on (they also
light up when on).  Which of the "CHANNEL ENABLED" switches needs to be
on is determined by how field service connects the disks to the controller.
These are push-button switches which lock into place, so that once set
they never have to be touched again, even across power failures.

When it is necessary to examine the 8000 controller, the back door is
opened revealing a maintainance panel with many switches and lights.
Most of these are for field service's use, but a few notes should be
given here to enable operators to cope with problems.

There is a selector switch labeled "MODE" at the right side of the
maintainance panal.  If it is in the rightmost "NORMAL" position, then
all other switches on the panal are disabled (as a safety feature).
To allow the other switches to work, the selector would be switched
to the "FE NORMAL" position.  This affects the operation of the 8000
in no way, except to allow other switches to work.  (IE, it will not
affect I/O operations to the disk).

There is a selector switch in the left center of the panel labeled
"ENTER/DISPLAY".  This switch selects which kind of information is
displayed in the LEDs immediately above, labeled "ADDRESS/CHECK/INLINE
DISPLAY".  The normal position of this switch is in the "INLINE" position,
where it displays a checksum of the microcode.  Other useful positions
of the switch are the "CHK1" and "CHK2" positions, which display certain
errors detected by the 8000.  Changing this switch does not affect
the operation of the 8000 in any way, except for changing the data
displayed in the LEDs.

The LEDs themselves are a row of 18 bits, labeled "P", "0", "1", etc
up to "15", "P".  The actual data bits are the numbered bits, and in
what follows the bits labeled "P" are ignored.

When the microcode is loaded and running properly in the 8000 controller,
and the "ENTER/DISPLAY" switch is in the "INLINE" position, bits "0" and "1"
should be lit, and bits "2" through "15" should be off.  If this is not true,
then the microcode in the 8000 is invalid and should be reloaded as
described below.  The microcode should also be reloaded if the indicator
labeled "CLOCK STOPPED" is on, or the "READY" indicator is off (both in
the top right of the maintainance panel.)

To reload the microcode of the 8000 controller, you have to put the "MODE"
switch into the "FE NORMAL" position, and flip the "RESET" switch which
is at the bottom of the maintainance panel.  This stops and resets the
8000 controller.  Then flip the "IMPL" switch in the top left of the panel.
This should start a sequence of events which will load the microcode
from the floppy drive, and start it.  This process is indicated by the
LED labeled "MPL ON" being lit in the top left of the panel.  After a
period of time about 30 seconds long (during which nothing much seems
to happen), the "MPL ON" light goes back off and the controller should
be ready.

If this procedure fails, you can try powering off and on the 8000
controller using the "POWER" switch on the top right of the maintainance
panel.  When power is restored, the 8000 automatically tries to load
itself, a process which takes several minutes.  During this time you
have no need to use the "RESET" and "IMPL" switches.  The RP20 disks will
also be shut off by this procedure, but they should come back on also.
If everything fails, you should call field service.

When the "ENTER/DISPLAY" switch is positioned to either "CHK1" or
"CHK2", and the LED display has any of the bits "0" through "15" lit,
this indicates a malfunction in the controller, and field service
should be called to fix it.

The 8000 controller must be tailered to your disk configuration.  Before
any change is made to the number of disks connected to the controller,
the microcode must be rewritten by field service to take into account
the changes.  Otherwise, new disks will not be seen, and UDBs will still
be built for nonexistent disks.  Therefore if there is ever a problem
where new disks are not seen by the system, suspect that the microcode
was not rebuilt to handle the new disks.

The 8000 controller has a unit number associated with it, which is
selected by microswitches inside the unit.  Field service should set
the controller number to the proper value depending on whether or not
the disks the 8000 controls are to be dual ported or single ported.
If the disks are single ported, the controller number should be 0.
If dual ported, then the two 8000 controllers which connect to the same
dual ported disks should have the same number greater than 0.  Every
pair of dual ported controllers has to have a different number.  This
is because the monitor uses the drive unit numbers to determine how
dual porting is set up, and the controller number is the high order
four bits of each drive's unit number.

The RP20 disks
______________

Each RP20 disk comes in a box which contains two spindles.  Even though
the two disk spindles are contained in one box, they are distinct.  That
is, each spindle is a separate disk drive as far as the monitor is
concerned.  The two spindles have different unit numbers, and can belong
to different structure if desired.  (However, it is obviously a good
idea to not split two pack structures across two RP20 units.  There is
more reliability in staying within one RP20 drive).

There are two kinds of RP20 drives.  There are the "A" units, and the
"B" units.  The "A" units contain power supplies and maintainance controls
which the "B" units do not contain.  There must be at least one "A" unit
for each three "B" units, since the "B" units get their power from the
"A" unit.  However, to the monitor there is no difference between these
two kind of units, they act identically as far as I/O is concerned.

The "A" units contain a couple of power switches in the leftmost door of
the unit.  These power switches control power to that unit and all "B"
units using that "A" unit as their power supply.  Throwing the switch to
the "OFF" position will power down the drives.  Throwing the switch to
the "ENABLE" position will allow the drives to be powered up, but does not
actually power them up.  You have to hit the "POWER ON" switch to actually
power the drives on.  The "POWER ON" switch becomes lit when the power is on.

Each RP20 spindle has a set of switches which control that unit, and
an indicator saying whether or not the unit is ready.  The switches
are as follows.  The switch labeled "START" and "STOP" is used to spin
the pack up and down.  When the switch the in the "STOP" position, the
disk becomes off-line and stops rotating.  (However, the fans continue
to run).  When the switch is in the "START" position, the disk spins
back up and comes on-line if possible.

The on-line state is indicated by the green "READY" indicator being lit.
This indicator will flash whenever a positioning operation is done for
the unit, and is therefore a sort of "busy" indicator saying that the
drive is being used currently.  However, notice that the transfer itself
does not make the light flash, only the positioning operations.  So I/O
can be occurring and you could not tell by examining the light.
This light is not a switch, so pushing on it does nothing.

The switch labeled "ATTN" is used to cause an asychronous interrupt
for that drive.  This is used to inform the monitor that a drive is
available for use.  If the drive was powered up while the monitor is
running, hitting this switch should not be necessary, since the drive
will give asychronous status by itself when it comes on-line.
However, under certain circumstances it will be necessary to hit
the "ATTN" switch before the monitor will acknowledge that the drive
is on-line.  In particular, if the drives were already on-line, but
the DX20 microcode was not running when the monitor was loaded, then
this switch would have to be hit for each drive before the monitor
knew about their existance.  This switch should NOT be used indiscriminately,
since hitting this switch while a transfer is in progress can cause problems.
Only use the switch when the unit is known to be idle.

The switch labeled "R/W" and "READ" is used to write-protect the drive.
The normal position is the "R/W" position, which allows data to be written
to the drive.  When in the "READ" position, nothing can be written to
the drive.  You should not write-protect drives which the monitor is
using, since it is necessary that the monitor be able to write to disks.
(You would use the "READ" position when diagnostics are being run on
the system, for example, not during timesharing.)  If the monitor
complains about "XWBERR" BUGCHKs (Index block write errors), it is possible
that one of the disks was left write-protected.

The final switches for each drive are the "DUAL PORT" switches, one
of which is the "X INTERFACE" switch and one of which is the "Y INTERFACE"
switch.  These control whether or not the unit can be accessed from the
two controllers it could be connected to.  One switch controls the first
port, and the other switch controls the second one.  The "ENABLE" position
allows access by the port, and the "DISABLE" disallows it.

			NOTE
Currently these switches have no function.  I don't know if they
will ever work.  It depends on what the hardware guys can do to make
them work.