NEC PC-9801VX – SCSI Devices

20Oct/222

NEC PC-9801VX – SCSI Devices

So, I've gotten my PC-9801VX to power-on, boot a floppy disk and then initialise the 486 upgrade... the next step was to get a HDD attached. Luckily, the unit already came with both SASI and SCSI cards, so I just had to choose one and connect things. SCSI was chosen, as I don't even know what SASI is and, perfectly by chance, I'd purchased an external 4.3gb SCSI HDD with the matching HD50 plugs!

Upon searching the usual boxes'o'junk for a cable, I attempted to plug the unit in and, to my surprise, the connector on the SCSI card wasn't actually HD50.

Turns out it's a mini-centronics HPCN50! You can learn all about SCSI connectors over here. It seems this connector type is very popular amongst PC98s. With this new information, I went scouring the web for an adapter. I found one from my usual favourite seller in NSW (RetroShopBox on eBay) and then also another full SCSI cable (HPCN50 to HD50) from the UK... but that was to take a lot longer to arrive.

I adjusted the HDD to SCSI ID 0 and, with everything connected, booted the IPL disk and then MS-DOS 6.20 Disk #1. The installation was painless, thanks to the Gotek, and before long the machine rebooted and failed miserably. This was due to MS-DOS 6.20 trying to start without the 486 Accelerator initialised and so I rebooted and installed that via the Installation disk. Before long, the machine had rebooted into DOSSHELL!

Removable Media

I grabbed my nearest Magneto-Optical drive and chained it onto the SCSI bus. It happened to be set to ID 6 and I just left it as-is and attempted to boot. Before long it threw the following error:

No system files!

To add insult to injury, it just continued to emit a high pitched squeal. Seems it thinks/knows this is a removable drive and expects removable media to be bootable. The disk in there certainly wasn't... I didn't even know what was on it.

Just for fun, I slapped in the IPL disk, installed DOS, installed the accelerator and then voila!, the disk started booting.. But the fun didn't last long. It failed with an error initialising MSDOS.SYS? How does that even fail?

No matter of mucking around got me further... Until I switched the MO's SCSI ID from 6 to 1. I had no idea why, but on ID 1, the MO booted to a command prompt! Unfortunately, once booted, I couldn't get to the internal HDD. The MO was mounted as drive A: and the floppies were mounted straight afterwards. No HDDs to be seen.

I had initially expected this unit to show up as a second HDD, so was a little perplexed as to how to make it act as one. A few emails back and forth from Adachi-san saw me realise that I either had to configure the drive into HDD mode, or force the SCSI controller to treat it like a HDD.

The SCSI controller is a TEXA HA55-BSW and, whilst booting, there's an initialisation screen that shows the devices found on IDs. During this process, there's no hint that it's able to be configured. After a little bit of googling, it turns out it can be configured, but only if you hold down the T and S keys at the same time whilst it's initialising.

Inside the configuration menu, you'll find drive options in the second choice. From here you can tick through the IDs and set the parameters accordingly.

I happened to find that the drive type could be set to MO Small Image and, well, this worked! I now got to the SCSI boot menu instead of just booting directly from the MO.

From here I booted into DOS on the main HDD at SCSI ID 0, but I still could only see that HDD (and other partitions on that SCSI drive), and no other SCSI devices. After a few more emails, it turns out there's a requirement with PC98 SCSI IDs: they need to be consecutive! That explained the issue above with MSDOS.SYS, but not this new one. Adachi-san also passed me a formatter that could format 230mb MOs up to 218mb and I went for it. Actually, it was obvious that the format was wrong as this is how the MO showed in the SCSI boot menu:

Similar to USB keys of nowadays with multiple partitions, this MO has been partitioned+formatted in "removable mode" and therefore shows up corruptly in HD mode. I re-partitioned and re-formatted the drive in the current HD mode with (RMUTL (Now MOUTL) from Adachi-san, received 218mb free and drive C appeared! Yesssss...... We can now copy from MO to HDD.

Thanks to my MO USB drive on my main machine, I could start expanding HDI files onto MOs and tinker...

CD-ROMs

I thought I might have needed the latest CD Drivers from archive.org, but DOS 6.20 just installed NECCDB.SYS and MSCDEX.EXE and my SCSI CD drive was mounted! I could even list the contents of the CD in the drive! Looking more-closely, it's actually an NEC CD-3010A which is somehow covered by the driver installed. Note that upon installation, DOS copies the driver it wants to use to the DOS folder as NECCD.SYS. Just match the sizes to determine which one it's actually using.