Editing Apple IIc (section)

==Revisions==
The Apple IIc was in production from April 1984 to August 1988, with minor changes. These modifications include three new ROM updates, a bug-fix correction to the original motherboard, a newly revised motherboard, and a slight cosmetic change to the external appearance of the machine. The ROM revision for a specific Apple IIc is determined by entering the Applesoft BASIC programming language and typing in the command {{code|PRINT PEEK (64447)|basic}} which returns the value indicating the particular ROM version.<ref>{{cite book| url=https://archive.org/details/Apple_IIc_Technical_Reference_Manual/page/n3/mode/1up |title=Apple IIC Technical Reference Manual |publisher=New York: Addison-Wesley |year=1987 |page=xxiii-xxv |isbn=0-201-17752-8 |oclc=17806974}}</ref>

===Original IIc (ROM version '255')===
The initial ROM, installed in machines produced during the first year and a half of production, is 16&nbsp;KB in size. The only device which can be connected to the disk port is (one) external 5.25-inch floppy drive; software can be booted from this external drive by typing the command {{code|PR#7}}. The serial port does not mask incoming linefeed characters or support the [[software flow control|XON/XOFF]] protocol, unlike all later firmware revisions. There is no self-test diagnostic present in this ROM; holding down the {{keypress|solid-Apple}} key during cold boot merely cycles unusual patterns on screen which serves no useful purpose or indication of the machine's health.

===Serial port timing fix===
Serial ports on Apple IIc motherboards manufactured before December 1984 are 2.9% slower than the [[Electronic Industries Association]] standard, greater than the permitted plus or minus 2% variance. Non-Apple modems with speeds greater than [[300 baud]] are incompatible with the ports.<ref name="linzmayer198412">{{Cite magazine |last=Linzmayer |first=Owen W. |date=December 1984 |title=Apple cart; using a parallel printer with the IIc, an RGB interface, a speed-up card, and the problem with modems. |url=https://www.atarimagazines.com/creative/v10n12/205_Apple_cart_using_a_paral.php |access-date=2025-01-31 |magazine=Creative Computing |page=205}}</ref> The motherboards derive the serial timing through a 74LS161 [[Transistor-transistor logic|TTL]] logic chip. This causes some third-party modems and printers, which operated at 1200 baud or faster, to function improperly. Slower serial devices operating at 300 baud or less are unaffected, as well as some faster devices which can tolerate the deviation. The solution to ensure all devices are compatible is to replace the TTL chip with a 1.8432&nbsp;MHz crystal oscillator (next to capacitor C19) during manufacture. Apple swapped affected motherboards for users who could prove they had an incompatible serial device (e.g. a third-party 1200-baud modem which presented problems; not all do).

===UniDisk 3.5 support (ROM version '0')===
This update, introduced in November 1985, doubles the ROM firmware in size from 16&nbsp;KB to 32&nbsp;KB. The new ROM supports "intelligent" devices such as the [[Macintosh External Disk Drive|Apple UniDisk 3.5]]-inch (800&nbsp;KB) floppy drive and Smartport-based hardisks, in addition to an external 5.25-inch floppy drive. A new self-test diagnostic is provided for testing built-in [[Random-access memory|RAM]] and other signs of logic faults. The Mini-Assembler—absent since the days of the [[Apple II Plus]]—returned, and new Monitor "Step" and "Trace" commands. The upgraded ROM adds rudimentary support for an external AppleTalk networking device. When attempting to boot virtual slot 7, users see "APPLETALK OFFLINE", but no compliant device was ever released. The upgrade consists of a single chip swap and minor motherboard modification, which Apple provided free only to persons who purchased a UniDisk 3.5 drive. A small sticker with an icon of a 3.5-inch floppy diskette was placed next to the existing 5.25-inch diskette icon above the floppy drive port indicating the upgrade.

===Memory Expansion IIc (ROM version '3')===
Introduced in September 1986 simultaneously with the [[Apple IIGS|Apple II<small>GS</small>]], this model introduced a new motherboard, new keyboard, and new color scheme.<ref>{{Cite web |url=http://docs.info.apple.com/article.html?artnum=790 |title=Apple IIc (Platinum): Mouse Moved from Slot 4 to Slot 7 |access-date=February 2, 2008 |archive-url=https://web.archive.org/web/20080208145628/http://docs.info.apple.com/article.html?artnum=790 |archive-date=February 8, 2008 |url-status=dead }}</ref> The original Apple IIc has no expansion options and required third-party cards to perform various hardware tricks. This can be done by removing the CPU and MMU chips and inserting a special board into these sockets, which uses bank switching to expand memory up to 1 Megabyte ([[Random-access memory|RAM]]). This is similar to the function of the slots in the original Apple II and II+, and the auxiliary slot in the Apple IIe. The new motherboard has a 34-pin socket for plugging in memory cards directly, which allows for the addressing of up to 1&nbsp;[[megabyte]] (MB) of memory using Slinky-type memory cards. The onboard chip count was reduced from 16 memory chips (64K×1) to four (64K×4). The new firmware replaces the code for the cancelled AppleTalk networking device with support for memory cards. Bumping out the non-supported AppleTalk functionality, memory now lives in virtual slot 4, and mouse support moved to slot 7. The new keyboard no longer has the rubber anti-spill mat and offers generally more tactile and responsive keys that feel more "clicky". The color of the keyboard, floppy drive latch, and power supply cords are light grey and not "Fog", matching the new Platinum color scheme of the [[Apple IIGS|Apple II<small>GS</small>]]. The case style is still [[Snow White design language|Snow White]]. Owners of the previous IIc model were entitled to a free motherboard upgrade if they purchased one of Apple's IIc memory expansion boards; they did not receive the new keyboard or the cosmetic changes.

===Memory Expansion fix (ROM version '4')===
In January 1988, a new ROM firmware update was issued to address bugs in the new memory-expandable IIc. Changes include better detection of installed RAM chips, correction of a problem when using the serial modem port in terminal mode, and a bug fix for keyboard buffering. The ROM upgrade was available free of charge only to owners of the memory expansion IIc. This was the final change to the Apple IIc,a nd superseded that September by the '''[[Apple IIc Plus]]''' (identified as ROM version '5').