Apple IIc ROM Versions
Apple IIc ROM Versions is a short community document, published via Apple2Online with no named author, covering the four Apple IIc firmware revisions and the hardware changes that accompanied them. It is not an Apple publication and is identified as a secondary source wherever this wiki cites it.
What is in it
[edit | edit source]- 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 ran about 3 per cent slower than the specified minimum, which made some non-Apple modems and printers at 1200 bit/s or above 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 show an incompatible device.
- Summaries of ROM 255 (original, 16 KB), ROM 0 (UniDisk 3.5, 32 KB, November 1985), ROM 3 (Memory Expansion, September 1986) and ROM 4 (Revised Memory Expansion, January 1988).
- The chip-count reduction on the Memory Expansion board, from sixteen 64K×1 devices to four 64K×4 devices, and the 34-pin memory card socket that board introduced.
Download: Apple IIc ROM Versions.pdf