PORTIBM PC Portable (uses same BIOS as XT) 0090-009F - PS/2IBM PS/2, any model - POS (PROGRAMMABLE OPTION SELECT) 0090 ?? Central arbitration control port 0090 RW POSTsee Power-On Self-Test diagnostic code (most PS/2IBM PS/2, any model with ISA(Industry-Standard Architecture) The expansion bus used by the IBMInternational Busiuness Machines PCIBM PC/ATIBM PC AT. See also EISA. bus) 0091 R- Card selection feedback bit 0 set when adapter addressed and responds, cleared on read 0092 RW PS/2IBM PS/2, any model system control port A (port B is at PORTIBM PC Portable (uses same BIOS as XT) 0061h) (see #P0415) 0094 -W system board enable/setup register (see #P0416) 0095 -- reserved 0096 -W adapter enable / setup register (see #P0417) 0097 -- reserved Bitfields for PS/2IBM PS/2, any model system control port A: Bit(s) Description (Table P0415) 7-6 any bit set to 1 turns activity light on 5 unused 4 watchdog timout occurred 3 =0 RTCsee Real-Time Clock/CMOS(Complementary Metal-Oxide-Semiconductor) A type of integrated circuit design known for its low power consumption. security lock (on password area) unlocked =1 CMOS(Complementary Metal-Oxide-Semiconductor) A type of integrated circuit design known for its low power consumption. locked (done by POSTsee Power-On Self-Test) 2 unused 1 A20(Address line 20) The 80286 and higher CPUs allow addresses in real mode to extend slightly beyond the one megabyte mark, which causes an incompatibility with some older programs which expect such addresses to wrap back to the beginning of the address space. For complete compatibility with the 8088, newer machines thus contain circuitry which permits the twenty-first address line (A20) to be disabled. The CPU then effectively has only twenty address lines in real mode, just as the 8088 does, and addresses which would extend beyond the one megabyte mark wrap to the beginning of the address space. See also High Memory Area, Real Mode. is active 0 =0 system reset or write =1 pulse alternate reset pin (high-speed alternate CPU(Central Processing Unit) The microprocessor which executes programs on your computer. reset) Notes: once set, bit 3 may only be cleared by a power-on reset on at least the C&T 82C235, bit 0 remains set through a CPU(Central Processing Unit) The microprocessor which executes programs on your computer. reset to allow the BIOS(Basic Input/Output System) A set of standardized calls giving low-level access to the hardware. The BIOS is the lowest software layer above the actual hardware and serves to insulate programs (and operating systems) which use it from the details of accessing the hardware directly. to determine the reset method on the PS/2IBM PS/2, any model 30-286 & "Tortuga" the INT 15h/87h memory copy does not use this port for A20(Address line 20) The 80286 and higher CPUs allow addresses in real mode to extend slightly beyond the one megabyte mark, which causes an incompatibility with some older programs which expect such addresses to wrap back to the beginning of the address space. For complete compatibility with the 8088, newer machines thus contain circuitry which permits the twenty-first address line (A20) to be disabled. The CPU then effectively has only twenty address lines in real mode, just as the 8088 does, and addresses which would extend beyond the one megabyte mark wrap to the beginning of the address space. See also High Memory Area, Real Mode. control, but instead uses the keyboard controller (8042). Reportedly this may cause the system to crash when access to the 8042 is disabled in password server mode (see #P0398). SeeAlso: #P0416,#P0417,MSR(Model-Specific Register) Additional, indirectly-accessible, registers containing control or status information about various aspects of the processor such as caches, performance counters, and the like. These registers, accessible via the RDMSR and WRMSR instructions, were added with the Pentium and later-model 486 processors. 00001000h Bitfields for PS/2IBM PS/2, any model system board enable/setup register: Bit(s) Description (Table P0416) 7 =1 enable functions =0 setup functions 5 =1 enables VGAVideo Graphics Array(Video Graphics Array) The video adapter introduced with the IBMInternational Busiuness Machines PS/2IBM PS/2, any model series of computers. =0 setup VGAVideo Graphics Array(Video Graphics Array) The video adapter introduced with the IBMInternational Busiuness Machines PS/2IBM PS/2, any model series of computers. 2 =1 enable integrated SCSI(Small Computer Systems Interface) A system-independent expansion bus typically used to connect hard disks, tape drives, and CD-ROMs to a computer. A host adapter connects the SCSI bus to the computer's own bus. See also ESDI, IDE. (PS/2IBM PS/2, any model M77) =0 setup integrated SCSI(Small Computer Systems Interface) A system-independent expansion bus typically used to connect hard disks, tape drives, and CD-ROMs to a computer. A host adapter connects the SCSI bus to the computer's own bus. See also ESDI, IDE. SeeAlso: #P0415,#P0417 Bitfields for PS/2IBM PS/2, any model adapter enable/setup register: Bit(s) Description (Table P0417) 7 activate Channel Reset on all slots 6-4 unused (1) 3 =1 setup adapter specified by bits 2-0 =0 enable registers 2-0 adapter slot select (000 = slot 1 ... 111 = slot 8) SeeAlso: #P0416