File:Apple IIc ROM Versions.pdf

Apple IIc ROM Versions (community document, author not named, published via Apple2Online).

A short account of the four Apple IIc firmware revisions and the hardware changes that went with them. It is cited on this wiki for one detail that does not appear in the other sources:

• The serial port timing fix. Original IIc motherboards, "manufactured between April and November 1984", derived the timing for both serial ports through a 74LS161 TTL counter. That timing was about 3 per cent slower than the specified minimum, which made some non-Apple modems and printers running at 1200 bit/s or faster misbehave; devices at 300 bit/s and below were unaffected. Apple replaced the TTL device with an oscillator in production and swapped affected motherboards for owners who could demonstrate an incompatible device.

It also summarises the ROM 255 (original), ROM 0 (UniDisk 3.5), ROM 3 (Memory Expansion) and ROM 4 (Revised Memory Expansion) firmware, and the chip-count reduction from sixteen 64K×1 devices to four 64K×4 devices on the Memory Expansion board.

This is a community document, not an Apple publication, and is identified as a secondary source wherever it is cited.

Mirror of ftp.apple.asimov.net at mirrors.apple2.org.za, documentation/hardware/machines.

Copyright the unnamed author / Apple2Online. Hosted here for reference and repair use only; no free licence has been asserted for it. Not public domain.