COMMODORE PLUS/4 INFORMATION 1-15-05 updates and/or corrections: 10-27-2021 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 peripherals 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 software, but I hope this info is helpful to other owners of Plus/4s. Here we go.... 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. 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 . 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 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 . TEDMON is started from BASIC by typing MONITOR & , and exited by typing X . 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 really need the Integrated Software Manual. Try www.funet.fi/pub/cbm/ for more information and schematics. 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. As an example, 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 selectchannel 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, CBM printers etc., the ones that work with the C64. The User port (RS-232) appears similar to the C-64 and uses 5 volt TTL level input/output signals. It will work with the Plus/4 modem but like the C-64, requires an adapter to interface true RS232 devices. CBM computers use a single-ended (+5VDC) TTL interface but true RS232 uses +/- 12VDC sources, so some kind of adapter must be used to interface PC devices. 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, and the pinout is as follows It is a mini-DIN, unlike the inline edge type connector of the C64 cassette interface. The pinout is shown facing the rear of the computer. It is important to get these pins correct if you are going to make an interface cable for your computer. A "mirror image" error in wiring will reverse power and ground connections and will likely damage your datassette and/or computer. Note the blank (unconnected) pin in the center of the connector. _____ sense / ground-----7 6 5-----write read -----4 [ ] 3----- motor drive +5VDC -----2 1----- ground ************************************************************************ 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 but not compatible. The pinout is as follows (viewed facing computer): ---v--- 9VAC ------|-0 0-|------ 9VAC | | +5VDC ------|-0 0-|------ Ground |_______| Note: you can use a standard power connector jack removed from a spare C64 motherboard to replace this unavailable square DIN type. It fits in the same place on the Plus/4 board without modification. Then you can use a standard C64 power supply, but as rare as the Plus/4 is, I would recommend a more reliable power pack than the old Commodore black brick. ************************************************************************ 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 ------8 | 7------ NC | Audio Out ------3 6 1--- Luminance & Sync Out (1VPP) ------5 4------ Comp Video Out 2nd Audio Out 2 (.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 and are the same as the joystick ports on the Commodore C16 and C116. Similar DIN plugs were used for Apple (MAC) computers on their printer interface cables. The following is a program to test the joystick ports of the Plus/4. 10 PRINT "JOYPORT 1="JOY (1) 20 PRINT "JOYPORT 1="JOY (2) 30 FOR X=1TO500:NEXT 40 SCNCLR:GOTO10 This BASIC program prints a pair of numbers on the screen. The numeric values depend on which direction the joystick is moved. Each position of the joystick or a pressed Fire button represents a contact closure of 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) 128 FIRE (JOYSTICK #2) Here is the pinout for the mini-DIN Joystick ports. It is shown facing the computer. Note the offset center pin! _____ Ground | ______ Right | | SELECT ------8 7 | 6------ Fire | +5VDC ------5 4 3------ Left Down ------2 1------ 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. NOTE: These joystick ports are not the same as a C64!!! From Rob Clarke: "One big big tip for your plus/4 is never use autofire joysticks without a properly buffered interface. If you have a simple mini-din to D-sub adapter, make sure it correctly wires /select (pin 8 ) to D-sub GND and never use anything but simple 5-pole joysticks, or you will eventually fry the latch on the TED." "The plus/4 & C16 do not use the ground line (pin 7) for the joysticks. If you look at the schematics, the up,down,left,right & fire lines are connected together between the two ports. The machine distinguishes between them by using a buffered data line (SELECT) instead of ground, with d2 going to port 2 and d3 going to port 1 (commodore never liked to make things simple.) This buffered data line is called /select on the schematics and is put on pin 8 of the joystick port." "If you do use ground, you *probably* will not damage anything but programs will not be able to tell which joystick is being moved. Two player games will just not work." AMIGAKIT information: If you already have an AmigaKit adapter cable, you can modify it to allow for two-joystick operation. Remove the shell from the mini-DIN plug by pulling it back and note the way the internal components fit together when you disassemble the plug. There will be some hot glue on the wires which must be removed enough to get to the wires. Desolder the yellow wire from pin 7 and connect it to pin 8 (the SELECT line). Since the +5VDC line is not used, you can disconnect it but it doesn't connect to anything via pin 7 of the 9 pin D-sub plug as joysticks don't use that pin. When you reassemble the plug, make sure you fit the shell notch or "dimple" above the three inline pins which is oriented upwards to insert the plug into the computer. The mini-DIN is a VERY tight fit into the Plus/4 and it must be inserted completely to work properly. One or more functions will not work if that plug is not fully seated. I found out the hard way. ************************************************************************* 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 a list of the the major ICs: U1 7360/8360 40 pin TED U2 7501/8501 40 pin CPU (microprocessor) U3 8551 28 pin ACIA (RS-232 interface) U5 & U27 6529B 20 pin I/O (single port interface) U19 251641-02 28 pin PLA U23 318006-01 28 pin BASIC ROM U24 318005-05 28 pin Kernal ROM U25 317055-01 28 pin function low ROM \___ 3+1 U26 317054-01 28 pin function high ROM / software Ray Carlsen CARLSEN ELECTRONICS... A leader in trailing-edge technology.