Subject: My first PDP-8

From: [email-masked] (PDP11 Hacker .....)
Date: Mon, 25 Apr 1994 17:19:00 GMT

Greetings PDP8-lovers...
  I was walking past the local PC shop today, and could hardly believe my eyes.
Among the disk drives and half-dead MS-DOS boxes was a DECmate 2. I quickly
bought it for 10 pounds.

Now, this is my first ever PDP-8 type of machine (although I may get a PDP8e
soon), and I know little about them other than having the instruction set, and
the Intersil 6100 data sheets. So, I have lots of questions. I'll apologise in
advance if any of these are directly off the FAQ list....
Note that I have the rainbow and PRO machines, and know a little about them.
So, you don't need to tell me the really basic stuff.
OK, on with the questions

1) The machine contains an RX50 drive, PSU, and a motherboard flat in the
bottom, like a rainbow. On the motherboard is a socketed chip labeled 6120, and
some other 40 pin IC's, all labeled the same. I assume the former is the CPU
(my Intersil databook is at home, and I don't remember seeing that chip in it,
only the 6100. What's the difference?). Oh, and a 7201 (serial chip I think),
6402's (UARTs), a 1793 (floppy controller), and a 8751 (microcontroller for the
floppy controller?), along with some CRT control stuff. Is the CRT controller
standard, and if so, where can I get a data sheet

2) There are 3 (empty) 40 pin connectors on the front of the motherboard. what
are these for, and does anyone know the pinout

3) Is the monitor cable the same as a PRO/rainbow mono monitor cable. I got an
LK201 and a VR201 with it, but no cable.

4) I don't seem to have a boot disk. Anyway, the manuals seems to imply that
the machine is a dedicated word processor. Where can I get a real OS boot disk
from (free (preferably :-)), or commercial), and what OS do I run?

5) Anything else you can tell me about this toy?
-tony

Bristol University takes no responsibility for the views expressed in this
posting. They are the personal views of the user concerned.

---

From: [email-masked] (Megan)
Date: Wed, 27 Apr 1994 13:11:04 GMT

>5) Anything else you can tell me about this toy?

I'd like to ask similar questions about a DECmate III.  It appears to have
an RX50 and a hard disk (RD3x?)

					Megan Gentry
					Former RT-11 Developer

---

From: [email-masked] (Charles Lasner)
Date: 29 Apr 1994 15:34:29 GMT

>an RX50 and a hard disk (RD3x?)

DECmate III doesn't have a hard disk.  However, you are describing a 
III+, which is a very different animal in a somewhat similar box.

With all of the recent inquiries about the DECmates, I guess it's time 
for a DECmate FAQ which focuses in on DECmate issues beyond those 
presented in Doug Jones' PDP-8 model FAQ.

Here's a thumbnail version.

DECmate I looks like a VT-100 with a few extra LED's on the keyboard.  
The standard model can't do anything without anything plugged in, but the 
standard configuration comes with RX02.  If you get either flavor of the 
dual USART serial interface (with or without the optional bit-stuff chips 
which allow SDLC, etc.) then you can make the otherwise bare box become a 
VT-100 which appears to not quite have all of the AVO option.  (14 lines 
in 132 column mode which is neither 12 as without or 24 as with.)

The standard version could be a pedestal-based RX02 pair, but in theory 
it was marketed also like the small -11 systems which had casters under a 
frame supporting RX or even RL drives.  There is even a quad RX02 (dual 
pair) version (I have it!).  A desk version could sit next to a cabinet 
holding RL02's if the RL278 option is present, etc.

There is no slushware, as all of the CP-memory routines are built-in.  
Only a handful of functions are implemented.

All RX02 and/or RL02-based PDP-8 software attempts to run here, as long 
as LPT: conventions of the VT-78 are assumed (as opposed to device 66; 
the VT-78 invented a new serial convention, but also supported the 
standard device 66 and even the weird -8/a variant parallel LA-180 
non-standard interface).  Of course all DECmates don't quite run -8 
software, but we've discussed that elsewhere, etc.

DECmate II shares the table-top box and overall configuration of the 
PRO-325 and Rainbow.  The standard machine comes with one pair RX50.  
Hard disk options are the RD51 controller plugged into the central slot 
connected to a variety of MFM drives which are meant to be housed in the 
top central area of the box.  Drives that were sold with the DM II were 
the 5 MB ST-506, 10 MB ST-412, and the 20 MB ST-225.  These were known as 
the RD50, RD51, and RD31 respectively.  Certain systems containing the 
ST-225 came with paperwork claiming they were only 10 MB, but customers 
quickly saw through this ruse.

As long as there isn't an MFM drive in the central area, an optional 
second RX50 pair can always be plugged in.

As long as there isn't a hard disk controller present, the RX78 option 
can be plugged in.  The RX78 can talk to one or two pairs of RX01/02/03.  
Cabling is via the standard connector associated with the DECmate I.  
(The documentation shows a DECmate I system being upgraded so that the 
pedestal of the RX02's holds up the DECmate II replacing the DECmate I box.)

All systems actually include three option slots, but the left (back view) 
is for the graphics option only while the right is for the APU or XPU 
options only.

There exist early systems incapable of supporting the graphics option, 
but this can be corrected by applying a substantial amount of hand 
soldering (add/deletes).  These systems also need a ROM upgrade to 
support the hard disk.  Many systems can only barely support the hard 
disk and should have the ROM upgraded to eliminate certain POST bugs.

The APU option is a Z80 and 64 KB memory.  It is used in a few WPS 
features and to run CP/M-80.  The XPU is a superset that also includes an 
8086 that is faster than the Rainbow and can be upgraded to a V30.  There 
are two memory options, 256KB and 512 KB.  The 512 KB version appears to 
have been able to support 1.0 MB but was never marketed as such.  Either 
version support the Z80 with some form of windowed memory sharing.  
MS-DOS 2.11 is available for the XPU versions.  (Note: IBM-PC 160 KB and 
180 KB diskettes are supported read-only on this system as well as the 
standard Rainbow MS-DOS format which is the same as the DECmate MS-DOS 
format.)

The graphics board comes in an early and late version.  Both are viable, 
but there are minor programming differences.  Most software 
self-configures around the differences, but some early diagnostics won't 
run on later boards.  (In any case, the option boards themselves are 
quite rare!)

The graphics board can talk to the normal mono monitor, and also 
supports the VR-241 color monitor as an option.  An obscure cable 
allegedly allows a color-only one monitor system.  (The WPS group claims 
that they won't support it, implying there is something to setup somewhere
that matters!)  In any case, the mono monitor can't have the text 
disabled, and the graphics interface can't have the color graphics output 
disabled.  All other video aspects can be gated to either output.  The 
GTE (Graphics Terminal Emulator) program exploits all of these modes, etc.

The DECmate III is housed in a small footprint box associated with the 
MicroVAX.  Early versions have marginal power supply problems.  Only an 
RX50 is present and there are no storage options.  There is an APU option 
that is compatible software-wise with that of the DM II.  There is also 
an optional graphics board that is quite rare.  Either of these can go 
into the two provided buss slots.  If the graphics board is present, then 
the color monitor is allowed; this is always a one-monitor system.  
Rumored to have been created but in any case never marketed is an 
MS-DOS-capable board that may have been a 286 and would have interfered 
with the VAXmate marketing.  There is also a special connector for a 
special version of the DEC Scholar 300/1200 Baud modem mounted internally.

The DECmate III+ superficially looks like the DECmate III, but uses a 
totally different board.  The mainboard supports a standard daughter 
board which is compatible with the RD51D hard disk option of the DM II.  
In the package is an RX33 TEAC floppy slowed down to be compatible with 
one/half of an RX50.  Also present is an RD31 or ST-225 20 MB MFM hard 
disk.  The external buss and slots are the same as in the DECmate III, 
and the same two options apply.

Clearly the board was meant to replace the DM III board since it can also 
be configured with a pair of RX33 drives and you can delete the hard disk 
daughter board.  Also the modem connector is present, but the associated 
chips aren't soldered in (but the lands are present!).

The developers of the never-marketed MS-DOS board reported that the 
ability to read the SDDD PC diskettes didn't work on the DM III+ because 
only the RX50 versions' controller supports this.

That's a short version.  If I work up a longer one, it'll get put on the 
sunsite archive, etc.

>					Former RT-11 Developer

cjl