I notice there is a lot of documentation on later models of PC-98 like PC-9821 or all those following the integration of the 386 CPU.
But early models, with Nec V30 CPU, are poorly documented on their bus (other than C-BUS), vidéo chip, and ram upgrade. For example, the range of PC-9801V / VM / U / UV / UX has no documentation on how to upgrade it.
There is some slots on motherboard. One is used for sound card and it's "not" C-BUS but more like than a large grey IDC connector. Is this connecor can host others extentions than a sound card ?
How to expand RAM ? early PC-9801 models has a limited amount of RAM. Often 256 or 384Ko. I notice there is some free IC sockets maybe for RAM, upgrade or option...
I try to answer myself to these questions in the following lines, but I hope someone with more knowledge can help :D
Now the photos :
The beast : fully functional PC-9801 with V30 CPU. I received this unit with no boot disk, HDD or screen. Few days after having suffer to booting up the thing, through floppies, I decide to install a SCSI HDD and a CD-ROM (DVD-ROM here)
- Front of this model (http://wellby.dyndns.org/dnl/img/pc-9801uv-front.jpg) : DIP switch is particularly tricky and model specific. Bad setup == no boot. On this model (PC-9801UV) DIP are from the left to the right :
assuming open (0) dip is up and closed (1) dip is down
SW1 :
1 - display resolution
--> open == 640x200
--> closed == 640x400
2 - superimpose mode (way of displaying japanese characters)
--> open == disabled
--> closed == enabled
3 - digital display
--> open == no
--> closed == yes
4 - IDs of floppies drives
--> open == Internal have ID 1 and 2 and external 3 and 4
--> closed == Internal have ID 3 and 4 and external 1 and 2
5 and 6 - RS-232 transfer protocol configuration
--> open - open == asynchronous transfer
--> open - closed == synchronous transfer with clocking
--> close - open == ST2 synchronization
--> close - close == BCI synchronization
7 - VF key
--> open == disabled
--> closed == enabled
8 - graphics capabilities
--> open == only 8 colors
--> closed == only 8 colors or 16 color among 4096
SW2 :
1 - LT mode (for PC-98 laptop)
--> open == normal display
--> closed == LT mode enabled (change the way of displaying graphics on screen)
2 - N88 basic operation
--> open == basic mode (normal operation)
--> closed == terminal mode (act as dumb terminal like TTY)
3 and 4 - text mode resolution (best is 80x25)
3 : columns
--> open == 40 columns
--> closed == 80 columns
4 : lines
--> open == 20 lines
--> closed == 25 lines
5 - erase RAM at reset
--> open == yes
--> closed == no
6 - internal HDD enabled (I don't know if it's for SCSI, SASI or whatever type of HDD interface)
--> open == yes
--> closed == no
7 - floppy drives rotation control (I think CRC control...)
--> open == no
--> closed == yes
8 - graphic controler frequency
--> open == 2.5Mhz
--> closed == 5Mhz
SW3 :
1 and 2 - type of floppy format dring boot process
--> open - open == auto detection for internal drives and assume 1.2mb for external drives
--> open - closed == auto detection for internal drives and assume 640kb for external drives
--> close - open == force to 1.2mb
--> close - close == force to 640kb
3 - DMA channels
--> open == enable DMA channel 0 only
--> closed == enable DMA channel 0 and 1
4 - type of display with LCD screen (not sure, but it can invert color for high contrast display on LCD screen)
--> open == LCD Reverse / PDP Normal
--> closed == LCD Normal / PDP reverse
5 - DMA clock
--> open == auto
--> closed == always high speed
6 - amount of base memory to use (this switch tell to OS what is the amount of base memory)
--> open == normal 512 or 640kb
--> closed == force base memory to 384 or 256kb
7 - unknow. On this PC-98 it is open.
8 - CPU type
--> open == NEC V30
--> closed == x86
- Back of this model (http://wellby.dyndns.org/dnl/img/pc-9801uv-back.jpg) : there is standard 25 pin D-sub RS-232 com port. Specific connector for mouse, floppy and printer. The analog RGB output can handle both progressive (480p) and interlaced mode (240p) depending on SW1-1.
B/W connector is for monochrome display. And an interesting "Digital RGB" connector. I wonder which type of signla it delivers...
- inside this PC-98 (http://wellby.dyndns.org/dnl/img/pc-9801uv-inside.jpg) : there is 3 removable boards. CPU board, sound card, and C-BUS hub. Back in the days, this is a beautiful piece of hardware beside western PC market with huge motherboard and no builtin video or sound.
- The motherboard with CPU board (http://wellby.dyndns.org/dnl/img/pc-9801uv-mobo-wcpu.jpg)
- The motherboard without CPU board (http://wellby.dyndns.org/dnl/img/pc-9801uv-mobo-wocpu.jpg)
Unknown C-BUS card : maybe a clever guy can find what is the purpose of this piece of hardware. I think this card may can drive some ECM machines...
- the board itself (http://wellby.dyndns.org/dnl/img/c-bus-unknow-ext-comp.jpg)
- solder side (http://wellby.dyndns.org/dnl/img/c-bus-unknow-ext-solder.jpg)
- connectors on the back (http://wellby.dyndns.org/dnl/img/c-bus-unknow-ext-con.jpg)
- The floppy drives (http://wellby.dyndns.org/dnl/img/pc-9801uv-flp-drives.jpg) : 3'5'' 360rpm 1.23mb drives. These give me a lot of headache. The best way to transfer data on an 1.23mb 3'5'' floppy is to find a 3 mode floppy drive. You can follow this useful thread (http://assemblergames.com/l/threads/writing-and-reading-pc9801-disk-images-for-real-machines.42533/).
- SCSI B55 IV C-BUS card (http://wellby.dyndns.org/dnl/img/c-bus-scsi-b55iv.jpg) : purchased this card after successfully booting from a floppy disk. New storage device... new headaches ! This card works, but after a lot of trial and errors. There is no diagnotic or setup included in the BIOS of this card. But after set the dip switch and boot option on PC-98 side (DIP SW2-6) I manage to boot from HDD and use SCSI DVD drive. You can download the DIP setting (http://wellby.dyndns.org/dnl/img/dip-scsib55iv.pdf) that I find after some experiment.
The C-BUS hub board. It working like ISA bus. Here there is 2 slot, but you can add more devices if you install a hub board with more than 2 slots. Unfortunately, the form factor is too small to up over 2 cards.
- C-BUS hub board (http://wellby.dyndns.org/dnl/img/c-bus-hub-comp.jpg)
- C-BUS hub board solder side (http://wellby.dyndns.org/dnl/img/c-bus-hub-solder.jpg)
The sound card based on YM2203 FM+PSG. No PCM. This chip have fantastic sounds and this is really pleasant to listen the ton of musics there you can found on this support. Specficaly FMP Music discs.
- the YM2203 sound card (http://wellby.dyndns.org/dnl/img/pc-9801uv-snd-ym2203-comp.jpg)
- solder side (http://wellby.dyndns.org/dnl/img/pc-9801uv-snd-ym2203-solder.jpg)
I have some examples recorded directly from this PC-98 :
- Gradius (http://wellby.dyndns.org/dnl/gk/snd/gradius2-return.mp3)
- Eve Burst Error (http://wellby.dyndns.org/dnl/gk/snd/eve_03.mp3) : nice bass with only FM, no PCM at all.
- Castlevania (http://wellby.dyndns.org/dnl/gk/snd/castle-beg.mp3)
- Popful Mail (http://wellby.dyndns.org/dnl/gk/snd/popful-1.mp3)
This sound card use a special connector (http://wellby.dyndns.org/dnl/img/pc-9801uv-snd-ym2203-con.jpg). I think this is just a C-BUS with specific pinout. Can we plug others devices than sound card on this connector ?
The CPu board. This is an interesting thing. I wonder if it possible to upgrade this one. This board contain CPU + RAM. RAM bank can be unplugged and upgraded but can't find ones on the Web... there is an empty socket, maybe for FPU...
- CPU board with RAM (http://wellby.dyndns.org/dnl/img/pc-9801uv-cpu-board-wram.jpg)
- CPU board without RAM (http://wellby.dyndns.org/dnl/img/pc-9801uv-cpu-board-woram.jpg)
- RAM modules (http://wellby.dyndns.org/dnl/img/pc-9801uv-ram-modules.jpg)
Let's talk about upgrade capabilities :
So, there is 3 way of extending possibilities.
- C-BUS (http://wellby.dyndns.org/dnl/img/pc-9801uv-mobo-c-bus-con.jpg) : there is memory/CPU upgrade through this one ? The speed may too slow to upgrade RAM or CPU through it...
- Sound card connector (http://wellby.dyndns.org/dnl/img/pc-9801uv-mobo-snd-con.jpg) : If it only C-BUS with another connector shape it's useless. It's a proprietary bus, than can accept device who upgrade this machine...
- CPU board connector (http://wellby.dyndns.org/dnl/img/pc-9801uv-mobo-cpucard-bus.jpg) : I think this is the best way to upgrade this model of PC-98. I found other CPU board like this (http://wellby.dyndns.org/dnl/img/pc-98-cpuboard.jpg). I think it's compatible but the form factor is not the same as present CPU board (http://wellby.dyndns.org/dnl/img/pc-9801uv-cpu-board-woram.jpg) (plus there is no RAM connectors). On the other hand connector seem to be the same.
Voila ! If any guy have more info on how to extend the PC-9801 models (V30 to 286) give your tips !