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From: Raymond Carlsen <rrcc@u.washington.edu>
Newsgroups: comp.sys.cbm
Subject: Commodore plus/4 info...
Date: Tue, 27 Jun 1995 09:05:23 -0700
Organization: University of Washington
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     I own a Commodore Plus/4 Computer, and was fortunate enough to get 
it with a working power supply and two books: The Users' Manual and the
Integrated Software Manual. Most people who own one of those "orphan" 
computers inherit the keyboard only, and are hard pressed to make it work
with little or no information and usually no periferals or software. The
Plus/4 came after the VIC-20 and the C-64 (about 1984), and is not
software compatable with either of those computers, although it does share
some hardware compatability. I decided to do a little digging inside my
Plus/4 and share whatever information I could. As a repair tech, I'm more
into hardware than software or programming, and I have no schematics or
disk software. I'm working by "seat of the pants", so standard disclaimers 
apply! I hope this info is helpful to other owners of orphan Plus/4s.

             **********************************************
     The Plus/4 comes up in Basic V3.5 with usable memory a little over
"60K bytes free" (The C-64 comes up with about 40K). Commands are similar
to the C-128 (DIRECTORY, HEADER, DLOAD, and COPY, for example) and such
things as reprogramming Function keys is possible. Obviously the Plus/4
requires software written for its' version of Basic, and memory locations
are specific to this model. For example, screen memory goes from location
3072 to 4071 (40X25 screen) and color memory from 2048 to 3047. Basic
starts at $8000. One source of "orphan" software is Jack Vanderwhite
(CEE-64 Alive!) PO Box 232115 Sacramento, CA. 95823 (916) 395-9773. He
posts frequently on the Internet Newsgroup: comp.sys.cbm. 
     The Plus/4 has several built-in programs stored on internal ROMs.
There is a Word Processor, File Manager, Spreadsheet, Graphics, and a ML
Monitor called TEDMON. The internal programs are initiated from the Basic
startup screen by pressing the F1 key. A SYS number is displayed... hit
-return-. This starts the word processor. Hold down the C= key and press C
to activate the Command mode, indicated by the "W>" prompt at the bottom
of the screen. Type TF (To the File manager) and -return- to go to the
"database". Similarly, typing TC (To the spreadsheet Command) and TW (To
the Word processor) will move to those ROM programs. Most commands are
two-letter combinations such as: LF (Load File) followed by -return-.
TEDMON is started from Basic by typing MONITOR -return-, and exited by
typing X -return-. GRAPHICS is part of the spreadsheet and allows
manipulation of charts and graphs. The GRAPHIC command entered from Basic
allows direct entry of HiRes graphics characters, drawing shapes and
controlling color. Because they are integrated, data can be moved across
the internal ROM programs. Obviously this is a simplified overview and is
intended only to get you started if you don't have the books. To properly
run these programs, you need the Integrated Software Manual. 
     The Plus/4 has three voices (or rather two programmable tone
generators and a noise generator). The first two output square waveforms
and # three outputs noise for special effects. To enable and play voice
#2... 
   10 VOL 7: REM sets volume level (0 is off)
   20 SOUND2,800,360: REM turns on #2, sets freq (about
      500Hz), sets the on-time (about 2 seconds).
             *********************************************
     The RF (TV) output is the same as on the C-64. An RCA jack on the
right side of the Plus/4 will connect, through an adaptor or switchbox, to
a standard Color TV set. There is a switch near the connector to select
channel 3 or 4. The color screen shows a 40 column display with border. 
     The Plus/4 serial port is identical to the C-64 and will work with
drives such as the 1541 and 1551 as well as CBM printers. 
     The User port (RS-232) appears the same as the C-64 and uses 5 volt
TTL level input/output signals. It will work with CBM modems such as the
1660 with no modifications, but like the C-64, requires an adaptor to
interface IBM type (Hayes compatable) modems. 
     The Memory Expansion Port (Cartridge port) is different from a C-64.
The connector looks similar, but has a total of 50 pins compared to the
C-64 which has 44. The SFS-481 Disk Drive and specific Plus/4 cartridges
were made to interface this parallel port. I was unable to find the
pinout, but I believe the Programmers Manual has that information. 
     The cassette port is a 7 pin Mini-DIN type similar to the joystick
ports but with a slightly different pin spacing. It works with the 1531
Datasette. I do not have the pinout. 
     The power supply for the Plus/4 is the same as the C-64, namely the
non-repairable "black brick" which outputs two voltages: 5 volts DC at
about 1 Amp, and 9 volts AC. Although some Plus/4s were built with the
round DIN type connector, most have a square 4 pin type, similar in
appearance to the C-128. The pinout is as follows (viewed facing rear of
computer): 
               
                 ----v---- 
     9VAC ------|-0     0-|------ 9VAC
                |         |
    +5VDC ------|-0     0-|------ Ground
                |_________|

            ***********************************************
     The video port (8 pin DIN) is nearly the same as the later models of
C-64, and monitors such as the 1702 (separated Y and C) will work with no
modifications. As with the C-64, a standard 5 pin DIN plug will also work
for monitors that accept only composite video and audio. The only
difference in the Plus/4 is -two- audio outputs, whereas the C-64 has an
audio -input- on one of those pins. The unloaded level on the second audio
output line is over 1 volt (PP). The lower level output connects
internally to the RF modulator as in the C-64. The pinout is as follows
(facing rear of computer): 

                          ________ Chroma Out
                         |           
                         |
         NC ------0      |      0------ NC
                         | 
  Audio Out ------0      0      0--- Luminance & Sync Out 
   (1VPP)                    
             ------0           0------ Comp Video Out
  Std Audio Out          0
     (.5VPP)              \________ Ground
 
              **********************************************
The joystick connectors are a departure from the "standard" 9 pin "D"
types that are used on the C-64 and the C-128. The 8 pin joy port
connectors on the Plus/4 are called Mini-DIN. They were used for the
joystick ports on the short-lived Commodore 16, and have also been used on
Apple (MAC) computers for many years and more recently for S-Video (4 pin)
on TVs and VCRs. The following is a small program to test the joystick
ports of the Plus/4. 

    10 PRINT JOY (1)
    20 PRINT JOY (2)
    30 GOTO10

This Basic program scrolls a number on the screen. The numeric value
depends on which direction the joystick is moved. Each position of the
joystick (or a pressed Fire button) represents a contact closure
(grounding one or more pins of the joy port). For example, when the
joystick is moved to the left, the number on the screen will go to 7. If
no switches are closed, the output number will be zero... 

Output   Function
------   ------------------
  0      NO SWITCHES CLOSED
  1      UP 
  2      UP AND RIGHT
  3      RIGHT
  4      RIGHT AND DOWN
  5      DOWN
  6      DOWN AND LEFT
  7      LEFT
  8      LEFT AND UP
 128     FIRE (JOYSTICK #1)
 135     FIRE (JOYSTICK #2) 

Here is the pinout for the Joystick ports. It is shown facing the rear of
the computer. Note the offset center pin! 
 
                                _____ Ground
                                |  ______ Right
                                | |
             Unknown ------0    0 |  0------ Fire
                                  |
              +5VDC ------0      0    0------ Left   
                                   
                 Down  ------0     0------ Up   

              ********************************************** 
     Since Plus/4 joysticks are so rare, standard CBM and Atari types
could be modified by cutting off the 9 pin "D" connector and installing
the 8 pin Mini-DIN male plug, or just changing the cable for one with the
Mini-DIN. Be careful with the wiring! There is a +5 volt source on those
joyports. You could damage ICs in the computer if you accidently short the
5 volts to ground. I would put a 100 ohm resistor on the ground-return
side of the switches, just to be safe. 
     The larger electronic parts houses sell Mini-DIN plugs and cables.
One source here in Seattle is Westlake Electronic Supply 1-800-523-8677
FAX: (206) 628-0508. They carry the GC Electronics line. The 8 pin
Mini-DIN is GC #33-938BU and the 7 pin cass. port plug is GC #33-937BU. A
less expensive 8 pin is GC #45-1160, and 7 pin is GC #45-1159. Two other
sources for DIN plugs are: Jameco Electronics 1-800-831-4242 and JDR
Microdevices 1-800-538-5000. Jameco sells a printer cable (Apple MAC) with
8 pin Mini-DINs on each end: part #10604. It sells for $4.95. That 6ft.
cable could be cut in half to make two 3 ft. joystick cables. 
            ********************************************
The proprietary IC chips used in the Plus/4 are apparently not used in any
other CBM equipment, and I know of no sources for these parts. The rest of
the chips are mostly LS TTL devices available anywhere. Here is the chip
complement: 

U1         8360R2      40 pin     VIC (40 Col NTSC)
U2         8501R1      40 pin     CPU
U3         8551        28 pin     ASIC (RS-232 interface)
U5 & U27   6529B       20 pin     ? ?  (parallel interface?)
U19        251641-02   28 pin     ROM \
U23        318006-01   28 pin     ROM |
U24        318005-05   28 pin     ROM |--- Built-in programs
U25        317055-01   28 pin     ROM |
U26        317054-01   28 pin     ROM /
