Changes to PSA Code

This list reflects some of the major changes to the PSA Code to support the BIOS on the HP palmtop. Effort has been made to maintain PC and HP 95LX compatibility in the user interface (inputs,outputs, and resource utilization) for BIOS routines that provide identical functionality in other HP palmtops. A number of additional non-standard BIOS services have been added to support features unique to HP palmtops.

• Reset Power On code is changed so that turning the machine on causes the machine to return to
  the application that was running before the system was powered down.

• Int 02h Nonmaskable interrupt (NMI).

  This interrupt is invoked in the IBM-XT when a RAM parity error occurs. It is invoked
  on the HP palmtop by the Low Power interrupt (LPI) or the Module Pulled interrupt (MPI).

• Int 05h Print Screen interrupt.

  The HP palmtop Print Screen service prints the contents of the active display page.

• Int 06h General Purpose hook.

  On the HP 95LX this hook was used for Low Power processing only. On any other HP palmtop,
  this hook is provided in several additional locations to permit applications to intervene
  in certain processing.

• Int 07h The HP palmtop BIOS installs a special Int 07h handler on power-up. Certain DOS
  applications do not use the equipment check to determine whether or not a numeric
  coprocessor is present. Instead they attempt to execute certain coprocessor instructions.
  Because of the configuration of the embedded 80186 CPU in HP palmtops, attempted execution
  of numeric coprocessor instructions will cause ESC Interrupts (Int 07h) to be generated.
  Without the default Int 07h handler supplied by the BIOS, numeric coprocessor instructions
  will "hang". The default Int 07h handler supplied by the BIOS "decodes" numeric coprocessor
  instructions, causing them to be skipped. This enables most applications to successfully
  determine that a numeric coprocessor is not present.

• Int 08h IRQ0 - Timer Hardware service.

  The Timer0 service was modified to add display window control via the menu-arrow key
  sequences.

• Int 09h IRQ1 - Keyboard interrupt.

  Int 09 was modified to support Fn key translations, and Mute key translations.

• Int 0Ah IRQ2 - Hornet Miscellaneous interrupt.

  Display Cursor Update, RTC, Timer1, RX, Ring Detect, Keyboard, IR, and several GPIO lines
  can be the source for this hardware interrupt. This is a reserved interrupt in the IBM XT.

• Int 0Bh IRQ3 - Unused (GPIO[24:26] Pads if properly configured).

  This is the COM2 interrupt in the IBM-XT.

• Int 0Ch IRQ4 - UART interrupt.

  This is the COM1 interrupt in the IBM-XT.

• Int 0Dh IRQ5 - Unused (GPIO[24:26] Pads if properly configured)

  This is the fixed disk interrupt in the IBM-XT.

• Int 0Eh IRQ6 - Ready/Change (GPIO[24]) interrupt.

  This is the diskette interrupt in the IBM-XT.

• Int 0Fh IRQ7 - Unused (GPIO[24:26] Pads if properly configured).

  This is the LPT1 (printer) interrupt in the IBM-XT.

• Int 10h Video services.

  MDA and CGA functions were modified for the "Hornet" hardware IC. Several non-standard
  services added.

• Int 13h Disk services.

  Modified to work with a RAM disk.

• Int 14h Serial Port services.

  Original PSA serial port services were modified to support the new 9-pin connection provided by
  the Hornet chip.

• Int 15h System services (Obsolete cassette control in XT).

  Most of Int 15h has been modified.

• Int 16h Keyboard services.

  This interrupt was modified to trap an [ON] key press while machine is running. Several hot-key
  sequences were added for display tuning control. Int 16h also invokes light sleep code as a power-saving feature.

• Int 17h Printer services.

  This interrupt was modified to work with a serial printer. The HP palmtop observes XON/XOFF
  flow control.

Int 19h Boot service.

HP palmtops boot DOS from ROM.

• Int 1Ah Time of Day services.

  Support of real time clock, including the capability of setting an alarm, was added. The alarm
  is capable of turning on power to the unit. Nonstandard functions were added to set alarms to
  future date (avoids shelf storage turn-on for system time updates).

• Int 1Eh Set to a dummy IRET.

  This is the disk parameter table in the IBM-XT.

• Int 1Fh Graphics Character Table pointer.

  This points to the last half (chars 80h - FFh) of the default font in the currently active code page font
  (std 8x8, byte wide).

  The following PSA interrupt handlers were not modified:

• Int 11h Equipment Check service.

• Int 12h Get Memory Size service.

• Int 14h Serial Port service.

• Int 1Bh Keyboard Break Default handler.

• Int 1Ch User Timer Tick hook.

• Int 1Dh Video Parameter table