Connectors

• a cartridge/expansion port that allows full 6510 bus access - 50-pin edge connector
• two joystick/paddle ports, 8-pin mini-DIN sockets.
• a composite video and audio output socket - 8-pin round DIN.
• a UHF TV output socket - standard RCA connector
• a cassette interface running at 300 baud. Compatible with earlier PET "Datasette" units - 8-pin mini-DIN
• a "user port" for TTL-level RS232 signals. Can be used for modems, parallel printers and more - 24-pin edge connector
• a reset button
• a serial bus for CBM disk drives and parallel printers. Serial version of IEEE-488 - 6-pin DIN
• a power supply socket - on the Plus/4 it requires 5V DC and 9V DC from external PSU - 4-pin square-DIN. On the C16 the single-pin round DIN socket requires 9V DC @ 1A.

Technical Facts

• the TED (Text Editing Device) chip caused the C16 and Plus/4 computers to run slower in some mode, because it did not have a seperate Colour RAM to store its data. Instead it used the computer's main memory, which is accessed by both the CPU and TED.
• TED also handled the sound, omitting the brilliant SID chip as found in the C64. TED, however, was not as capable sound-wise, offering just 2 tone generators, although one of these could also produce distortion effects.
• The Plus/4 could run both the standard serial floppy drives (CBM 1540/1541) and it's own dedicated drive, the CBM 1550, which was much faster (400%!) due to its use of the parallel interface of the cartridge port. Commodore also produced the CBM 1542 which was just a repackaged 1541 in a grey case for people who didn't want to spend the extra money for the 1551. Since the 1551 disk drive is a parallel device, it actually connects to the Plus/4 and C16 via the expansion port, whereas the other disk drives are serial devices so they use the serial port.

Hover your mouse over this Plus/4 circuit board for a description of the components

Component details reproduced with friendly permission from Sothius' Home, www.sothius.com (shame you closed your site, Sothius, it was great! Ed)

Hover your mouse over this Commodore 16 circuit board for a description of the components

Component details reproduced with friendly permission from Sothius' Home, www.sothius.com

Trivia

• The Plus/4 was originally planned to be a professional business computer (as they already had their games machine in the C64). For this purpose, the machine had 'option ROM' sockets (similar to the Acorn BBC and Commodore's own PET-series). The Plus/4 came with four integrated programs on two ROMs - Tri-Micro's '3-plus-1' application suite, consisting of a word processor, spreadsheet, graphics tool and file manager.
• The Plus/4 was called the C264 during development, and was named 'Plus/4' due to the four built-in applications.
• The standard floppy drive for the C16 and Plus/4, the CBM 1551, makes use of the machine's cartridge port. This port has special disk I/O features for parallel data transfers, making it much faster than the 1540/1541 serial interface.
• You can bring up the built-in machine-language monitor tool when in BASIC, by typing in 'MONITOR' and hitting Enter.
• Earlier Plus/4s came with a round DIN socket for power, which allowed the use of the C64's power supply. This was later replaced with a 'square-DIN', for use with the 310200-09 power supply.
• Commodore never produced any RAM expansion solution to the C16, although several third-party companies produced them.
• Both the C16 and Plus/4 came with an enhanced version of BASIC - Commodore BASIC v3.5. This was a big improvement on the older version from the C64, and included specific commands for disk I/O and TED including control commands for graphics, sound and bank-switching. The later Commodore 128's BASIC v7.0 took this version as its basis although omitted the TED-specific stuff.
• You could actually connect two disk drives to the C16 and Plus/4 computers. The second drive cable attached to the back of the first cable.
• To hard reset a C16 or Plus/4, you press and hold RUN/STOP and CTRL, and press the reset button.