AT Compatible DOS Application

to PC-9800 Series

Considering Software Localization

September 1996
First Edition

Hardware

• Interrupt Controller

  AT compatible machines and PC-9800 use the same controller, but the I/O address, interrupt level and the devices that are connected to each level differs. On the AT compatible machines, the specific EOI (specifying the level used) is used, but on the PC-9800, non-specific EOI (20H) is more generally used.

• Timer

  On the AT compatible machines, counter #0 (system time) is constantly operating as an interval timer, but on the PC-9800, the interrupt is usually masked and it is not moving. The applications or the device drivers can program it as an interval timer, but it is not recommended. This is because there are no rules when used also as an interval timer. V-Sync interrupt may be used as an interval timer. However, when periodic interrupts are not necessary, use the time stamper which is provided.

• Real Time Clock

  Depending on the kind of PC-9800 machines, different real time clock is used, so there are some that has the year and there are some that doesn't. Thus, it is recommended to use the BIOS's or the operating system's API functions to get the date and time.

• Keyboard

  Keyboard's hardware architecture is completely different.

  • Scan code is different.
  • At key repeat, the scan code repeats "make" and "break".
    (On the AT compatibles, "make" is repeated and at the end, comes "break".)

  To make the Japanese input possible, you must use the API provided by the operating system. On the PC-9800, you cannot distinguish between left and right Shift key.
  Ctrl key is on the left side only.
  Substitute the GRPH key for the Alt key.

• Video

  PC-9800's standard video mode is 80x25 x 8 color text, and 640x400 x 16 color graphics. Text and graphics may be displayed on top of each other. In CGA text mode, by using this standard video mode, localization is easy. In the text mode of AT compatible machines, character's foreground and background color may be specified, but PC-9800 does not have this function. However, when text and graphics are stacked on top of each other, as mentioned earlier, this can be realized by using the graphics as the text's background color.

  To localize from VGA, 640 x 480 resolution can be realized by using the 256 color graphics mode. (To change to 256 color graphics mode, use the AVG driver.) The PC-9800 graphic accelerator is for Windows graphic acceleration, thus VGA compatible functions are not guaranteed to work. Also, since there is no VGA BIOS, to use it, you must directly access the chips. If you want to use the graphics accelerator, it is recommended to make the applications work on Windows.

• Serial Port

  PC-9800 serial port supports synchronous method in addition to asynchronous method. In asynchronous method, it is guaranteed to work up to 19200 bps transfer rate. In synchronous method, even more faster transfer rate is possible. Baud rate depends on the periodic rate that is set on the timer. The timer's speed depends on the bus clock. The value of the bus clock can be read from the parallel port.

• Parallel Port

  PC-9800's standard parallel port only has one status: Busy. When the printer is not connected, it stays at NonBusy (Ready). In this condition, the output data will be lost. To get around this, turn the strobe signal on then by watching the Busy signal for a certain time and seeing the Busy signal changing, you can be sure that the data was received. When the Busy signal does not change, the printer is not connected. When the hardware is directly manipulated, you cannot output to the remote printer, thus you must check if the printer is local or remote, before executing the above process. On the latest machines, they come with a bi-directional parallel port. By using this, you can use the same functions as the AT compatible machines.

• Mouse

  PC-9800 mouse has an interval timer as a hardware interrupt. This method is the same as the AT compatible bus mouse. The AT compatible's mouse hardware interrupt occurs only when the mouse has been moved.

• Floppy Disk

  Both AT compatibles and PC-9800 has the same device (NEC 765) as a base. However, PC-9800 also support the low density types. Individual drive's motor can be controlled independently on the AT compatible machines, but on the PC-9800, all drives at the same time will be controlled. On the PC-9800, the hardware interrupt of the floppy disk controller inputs a timer interrupt for motor control in addition to the interrupt from the floppy disk controller. Also, on PC-9800, interrupt occurs when the media is inserted and removed (attention interrupt). On AT compatible machines, the interrupt occurs only during the execution of the command, but please be cautious, because on the PC-9800, the interrupt occurs asynchronously even when the motor control timer or the attention interrupt is not executing the command. Since the PC-9800 floppy disk format has 1024 bytes/sector as standard, you should not access the floppy disk controller directly. If the API provided by the operating system is used, it does not depend on the format.

• Hard Disk

  PC-9800 uses SASI interface hard disk in standard, but on the latest machines, SASI interface is emulated by using the IDE interface. Therefore, it is not recommended to directly access the hard disk controller. This is the same with the SCSI interface. Since there are many kinds of SCSI interface controllers, it is hard to support all of them. This is same for AT compatible machines. 512 bytes is the standard sector length of the AT compatible machines, but the PC-9800 also supports 256 bytes.