NEC PC-9800 Quick Guide

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The PC-9800 keyboard has some equivalent keys with different names and some additional keys which are not found on the IBM-PC keyboard. Also, the keycodes returned to the main unit are different from the IBM-PC keycodes.

STOP Break
COPY Print Screen
VF1 - VF5 Application program function keys
NFER and XFER Used to interface with Kanji input
Kana Toggles Roman/Kana keyboard state

Floppy Disk

Both 5.25" and 3.5" systems are available. The system automatically recognizes when a drive is connected. The PC-9800 can access US format diskettes as shown below.
Disk Format Capacity PC-9800 Can... NEC DOS FORMAT Command...
360K IBM 362,496 read  
640K NEC 3.5" and 5.25" 649,216 read/write /6
720K IBM 3.5" 730,112 read/write /9
1.2M IBM 5.25" 1,213,952 read/write  
1M NEC 3.5" and 5.25" 1,250,304 read/write /M**
1.44M IBM 3.5" 1,457,664 read/write* /4


* Most PC-9821 systems can read/write, previous machines cannot.

** NEC machines can read/write IBM formatted 1.2MB 5.25" disks, but IBM computers cannot read/write NEC formatted disks. So if you format 5.25" disks on an IBM, then both PCs can read/write the disk.

Hard Disk

SASI, SCSI and IDE hard disks from 20MB to 2GB are supported.


Text Mode

The PC-9800 has a text display buffer RAM area where character codes and attribute bytes are placed. However, these areas are different from the IBM-PC in order to handle Kanji characters and different attribute byte flags. Any direct access of the text display buffer at 0xB800 or 0xB000 must be changed. PC-9800 uses 0xA000 for characters and 0xA200 for attributes. This represents the first text page in normal mode.

Eight (8) colors are available for the foreground setting. The reverse video bit toggles this color selection to the background color with black text. The text handling functions of Microsoft C are available in most Japanese C compilers.

PC-9800 Text Display Attributes:

bit 0 /ST secret, hidden
bit 1 BL blink
bit 2 RV reverse video
bit 3 UL underline
bit 4 VL,BG vertical line or simple graphics (toggled by F/F bit)
bit 5 B blue
bit 6 R red (monochrome display will be 8 level gray scale)
bit 7 G green

The H-98 and PC-9821 architectures extend the attribute to two bytes to support additional features such as separate foreground and background colors with selection from sixteen (16) colors.

Graphics Mode

There are two standard resolutions provided by the PC-9800: normal mode and high resolution mode with 16 colors available. The PC-9821 and some PC-H98 models have 256 colors standard. Optional hardware may be installed on other machines for 256 colors. The CRT interface uses an analog RGB monitor and can also produce digital RGB in normal mode.

The memory architecture and programming interface are different from IBM-PC adapters such as VGA and EGA. Programs written directly to video hardware must be modified. NEC recommends using the GRAPH.SYS driver provided with NEC DOS 3.3 for PC-9800 hardware independent programming. The PC-9821 provides the AVGDRV.SYS driver. The graphics handling functions of Microsoft C are available in most Japanese version compilers. MS Windows, OS/2 PM, and UNIX OpenDesktop also isolate your application from the video hardware.

NEC currently offers systems with graphics accelerators including Cirrus Logic, S3 and Matrox. Most can be configured through Windows drivers to run resolutions as following.

CG Window Fonts

Many graphics mode applications need access to character fonts. The hardware CG (Character Generator) Window fonts may be accessed directly in order to retrieve font bitmap patterns from ROM. These fonts are of fixed size. Rapid access is done through I/O ports or memory mapped RAM. Typically, a graphics application will access CG Window and transfer the resulting character bitmap font to the graphics display. For access to variable sized fonts, use the FONT.SYS driver.

Serial and Parallel Ports

Each PC-9800 comes equipped with one (1) serial and one (1) parallel port as standard equipment. The PC-9800 uses an 8251A device as its serial controller rather than the IBM-PC standard 8250 and compatible 16450 or 16550 devices. The I/O control registers and ports must be handled differently. Any access to standard IBM-PC serial I/O ports 0x3F8, 0x2F8, etc. must be changed. Likewise, standard parallel I/O ports 0x3BC, 0x378, etc. are invalid on the PC-9800. With version 6.0 of the Microsoft KK C compiler, the _bios_serialcom( ) functions are available. The newer PC-9821 systems can support up to 19.2Kbps.

Windows applications can use the same serial communications API on all platforms. However, only the newest PC-9821 support 19.2Kbps. Most machines support a maximum of 9,600bps.

Cables and Connections

There are many different printer, serial, and video connectors used on the PC-9800. Be sure to check that you have or are requesting the correct cable for the PC-9800 model you are using.


Interrupt control architecture in the PC-9800 is similar to that of the IBM-PC. Two 8259A compatible interrupt controllers are used in a cascaded design. However, the slave is cascaded to IRQ7 of the master rather than IRQ2 and the interrupt vectors are different. Consult the PC-9800 Technical Data Book - Hardware4 for additional information.

DMA Controller

Provides 4 channels of high speed data transfer between the memory and peripheral devices using a PD8237A-5 equivalent device. PC-H98 adds four (4) additional chanels and the capability to handle 32 bit addresses and transfers.

Adapter Card Expansion Bus

The original PC-9800 bus is called C bus and uses a different adapter board form factor, but with an edge connector signals similar to the ISA 16-bit peripheral bus design. Signals available are similar to the ISA bus expansion slot. These are detailed in the NEC PC-9800 Technical Data Book - Hardware4 .

In a design similar to the EISA bus, the NESA bus used in PC-H98 systems allows existing PC-9800 bus adapters to be used in the NESA slots. An additional connector is found on NESA bus cards in order to access the additional signals.

Some models of the PC-9821 have local bus video which enables a high speed graphics interface. This interface is used in the NEC High Resolution mode card and video accelerator based NEC Windows Accelerator cards. In addition, NEC is now shipping some models with PCI bus. New notebook designs have PCMCIA sockets and drivers.


Any calls to the IBM-PC BIOS must be changed to PC-9800 compatible calls or code.
IBM-PC BIOS Interrupt Name PC-9800 BIOS Interrupt
0x09 & 0x16 Keyboard 0x18
0x10 Video 0x18
0x13 Disk 0x1B
0x14 Serial Communications 0x19
0x15 System Services various
0x17 Printer 0x1A


The BIOS RAM area allows the BIOS to keep information regarding system status. While it includes items such as the keyboard buffer and current graphics mode, its layout is not like the IBM-PC BIOS RAM area at 40:0. Applications which have hardcoded BIOS RAM addresses must be changed in order to run on a PC-9800. If possible, these applications should use higher level DOS or BIOS function calls.


The NEC mouse BIOS provides access to the standard bus mouse hardware on the PC-9800. This BIOS interface is not the same as the Microsoft MS-Mouse interface. However, mouse drivers are available which do provide a standard Microsoft MS-Mouse interface. Logitech provides both NEC and MS-Mouse compatible drivers in their Japanese product. US applications which call the standard int33 interface can run without change using the Microsoft compatible driver. The NEC mouse driver implements some of the basic int33 calls in the same way such that software making only basic mouse calls may not need to be different in order to run under either mouse driver..

Other BIOS Interfaces

A Sound BIOS and GPIB BIOS are included which work with the NEC PC-9801-26 and PC-9801U-3 sound boards and the NEC PC-9801-29/K/N GPIB interface board respectively. The AVSDRV.SYS driver also allows access to the PC-9801-86 and PC-9801-73 sound hardware

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