Editing IBM PS/2 Model 25 (section)

=== Model 25 286 planar ===

The Model 25 286 planar uses an Intel 80286 at '''10 MHz with 1 wait state to system memory''' and a '''VLSI VL82C100 / VL82C101 / VL82C102 / VL82C103 / VL82C104''' chipset (the "Popular AT" PC/AT-compatible chipset by VLSI). The system supports up to 4 MB of RAM on '''two 30-pin "MMK" parity SIMM''' sockets (J9/J10) with a proprietary IBM pinout, and includes a '''VGA''' graphics subsystem driven by the IBM 15F6864 VGA gate array (ZM18) and the '''Inmos IMSG171P-35''' RAMDAC (ZM23).

Additional planar I/O on the Model 25 286:
* '''VLSI VL16C451''' &mdash; integrated UART + parallel port (ZM9).
* '''NEC D765BC''' &mdash; floppy disk controller (ZM19).
* '''Intel 8042''' &mdash; keyboard controller (ZM33), supporting the PS/2 keyboard and pointing device (PS/2 mouse) ports.
* '''27F4094 DISKGA''' &mdash; IBM disk/diskette gate array (ZM14), supporting the proprietary PS/2 single-cable floppy interface and the optional ST-506 hard drive interface.
* Crystals: Y1 = 14.318 MHz; Y2 = 25.175 MHz; Y3 = 20.322 MHz; Y4 = 20.0 MHz; Y5 = 48.0 MHz.
* The 286 planar adds a '''4-pin auxiliary power connector''' to feed the 16-bit ISA bus (not present on the 8086 Model 25), and a '''math coprocessor socket''' at ZM1 for an 80287.
* Battery-backed CMOS via the MC146818-equivalent RTC integrated into the VLSI chipset.