Editing Commodore Plus/4 (section)

== Hardware ==
[[File:Plus4 komplett.jpg|thumb|Commodore Plus/4 with accessories. Clockwise from top left: power supply, joystick, [[Commodore Datasette|1531]] tape recorder with tapes]]

=== Graphics ===

The [[MOS Technology TED|TED]] offered 121-color (15 colors × 8 [[Luma (video)|luminance]] levels + black) video, a [[Palette (computing)|palette]] matched only by the [[Atari 8-bit computers]] and the [[Enterprise (computer)|Enterprise]] at the time, and 320×200 video resolution, similar to many computers intended to be capable of connecting to a television.

The TED chip had identical resolutions and video modes to the [[MOS Technology VIC-II|VIC-II]] (bitmap or character graphics which could be high-resolution or multicolor), but lacked hardware [[Sprite (computer graphics)|sprites]]. Its sound capability was a two-voice [[Square wave (waveform)|square wave]] generator.

The first eight colors of the TED's palette are the same as the VIC-II, but colors 8-15 are different. It allowed each color except 0 (black) to be set to one of eight possible luminance levels, thus making 121 total colors possible.

The power-on default configuration places the screen memory at {{mono|$0C00}} and the color memory at {{mono|$0800}}. Color memory is integrated into the TED and there is no separate color RAM like on the VIC-20 and C64. Bits 0-3 of each byte in color RAM hold the color value and 4-6 hold the luminance. Bit 7 is a [[Flag (programming)|flag]] that sets blinking text. [[Bitmap]] mode is similar to the C64, however in hi-res mode the color RAM is used to supply the luminance values for each block (bits 0-3 the luminance for color 0 and 4-7 the luminance for color 1) while it is not used at all in C64 hi-res graphics. In multicolor bitmap mode, the same setup is used, but while on the C64, color RAM holds the values for color 3, on the Plus/4 it instead holds the luminance values for colors 1–2. Color 3 is instead global and obtained from the register at {{mono|$FF16}}.

The Plus/4's TED has several advantages over C64's VIC+SID. All TED [[Hardware register|registers]] that are available can be read and written. TED may realize the blinking cursor and the characters in the reverse-video mode. It may display 256 characters in the text mode. It may use graphics split by [[raster interrupt]] and show pictures at 320x288 resolution.<ref>{{cite web|url=http://plus4world.powweb.com/software/40x36c|title=The examples of Plus/4 graphics}}</ref> This, with [[Interlaced video|interlaced]] mode, makes it possible to show 320x496 images. In addition, the TED has 16 [[address line]]s, thus it can "see" the entire memory space of the computer unlike the VIC-II. The video buffers may thus be placed anywhere in memory and there are no mirrors of the character ROM to get in the way like on the C64.<ref>{{cite web|url=http://www.lemon64.com/forum/viewtopic.php?t=47356|title=The examples of Plus/4 graphics|date=8 April 2013 }}</ref>

=== Input and output ===

Commodore released a high-speed [[floppy disk]] drive for the Plus/4, the [[Commodore 1551]], which offered much better performance than the C64/[[Commodore 1541|1541]] combination because it used a [[parallel interface]] rather than a [[Serial_communication#Serial_buses|serial bus]]. The 1551 plugged into the cartridge port.

The Plus/4 had a built-in [[MOS Technology 6551]] [[Universal asynchronous receiver-transmitter|UART]] chip that could perform up to {{nowrap|19200 [[Bit_rate|bit/s]]}},<ref>{{cite web|url=https://archive.org/stream/run-magazine-35/Run_Issue_35_1986_Nov#page/n103/mode/2up|title=RUN Magazine Issue 35|date=November 1986}}</ref> unlike the C64, which emulated the 6551 chip in software.{{citation needed|date=January 2023}} This allowed the Plus/4 to use high-speed [[modem]]s without additional hardware or software tricks (the C64 required specially written software to operate at {{nowrap|2400 bit/s}}), at a time when 300- or 1200-bit/s modems were more common{{snd}} and Commodore never released a 2400-bit/s modem{{snd}} so this feature went largely unnoticed. The Plus/4's serial port is the standard Commodore user port used since the PET, featuring [[Transistor–transistor logic|TTL]] voltage which is incompatible with [[RS-232]]. This requires a [[voltage converter]] to use modems or other serial devices from non-Commodore vendors.

The Plus/4 keyboard had a separately placed directional "diamond" of four cursor keys, presumably more intuitive to use than the VIC's and C64's two shifted cursor keys.{{synthesis inline|date=January 2023}}

A reset button was added on the right side of the system, a feature lacking on the C64.

The Plus/4 also revived the built-in [[machine language monitor]] from the PET days, a feature missing on the VIC-20 and C64.

=== Specifications ===
[[File:Plus4 main board.jpg|thumb|Main board]]
[[File:Plus4 Interface.jpg|thumb|I/O ports]]

* CPU: [[MOS Technology]] [[MOS Technology 6510#MOS 7501/8501|7501/8501]], approximately {{nowrap|0.88 [[megahertz|MHz]]}} when the raster beam is on the visible screen and {{nowrap|1.77 [[megahertz|MHz]]}} ([[PAL]]) / {{nowrap|1.79 [[megahertz|MHz]]}} ([[NTSC]]) the rest of the time<ref name=DatorMuseum />
* RAM: {{nowrap|64 KB}}, of which nearly {{nowrap|60 KB}} (60671 bytes) is available to [[Commodore BASIC|BASIC]] users. There are known RAM expansions with {{nowrap|256 KB}} and 1 [[Megabyte|MB]]<ref name="circuit">{{Cite web|url=http://www.zimmers.net/anonftp/pub/cbm/documents/projects/memory/plus4/|title = /Pub/CBM/Documents/Projects/Memory/Plus4/}}</ref>
* ROM: {{nowrap|64 KB}} including [[Commodore BASIC|Commodore BASIC 3.5]], a [[machine code monitor]], and TRI-Micro's "3 Plus 1" (word processor, spreadsheet, database, graphing). It is possible to add up to {{nowrap|64 KB}} more ROM with [[ROM cartridge|cartridges]].
* Graphics: [[MOS Technology TED]] (TED 7360)
* Text mode: 40×25 characters ([[PETSCII]]). There are three text modes: standard, extended color, multicolor
* Graphics modes: 160x200 (multicolor, 2bpp, no sprites) / 320×200 (hi-resolution, 1bpp) at 121 colors (all can be visible at the same time)
* I/O ports:
** Tape connector (for [[Commodore 1531]] Datassette with {{nowrap|[[Mini-DIN connector#7-pin|7-pin mini-DIN]]}}; incompatible with C64, although adapters allowing the machine to use earlier and aftermarket datasettes were common.)
** [[ROM cartridge]] slot (incompatible with C64)
** Two [[Mini-DIN connector#8-pin|8-pin mini-DIN]] [[game controller]] ports (incompatible with C64)
** Commodore serial bus (compatible with C64)
** User port (for modems and nonstandard devices, incompatible with C64)
** [[Composite video]] connector including [[S-Video]] and mono audio signal (compatible with C64)
** [[RF modulator]] to TV antenna connector (compatible with C64)
* The power connector is compatible with C64 power supplies in some Plus/4s and takes the same 9V AC and 5V DC voltages, but uses a non-standard "Square DIN" plug, like the C128, in most Plus/4s.