Back to Hacking the GRiDCase 1500 series.
Most GRiDCase 1500 series computers use Storage Backplanes. The exception is the 1550 variants which have onboard IDE. These backplanes are daughter boards that interface between the mainboard and floppy/hard drives. Mainboard pinouts here for that. There are a number of different backplanes to support different drive configurations. During initialization the computer’s BIOS will query the backplane’s ID and then expect a certain combination of floppy and/or hard drives based on that.
Backplanes for Floppy, IDE, or combinations of either should work in any GRiDCase 1500 series (except 1550). Backplanes that support JVC interface hard drives are also dependent on an additional daughter board which not all mainboards support (must have a special connector).
- Known backplane ID’s and their configurations
- Backplane schematics
- How backplane identification works
- How to read the backplane ID
- What’s actually on the backplane?
Known Backplane ID’s and Configurations
This table lists known variants and supported configurations based on my research. Data sources are mostly from devices I own and data extrapolated from multiple GRiDCase BIOS ROMs. Some information cross references to GRiD replacement part lists, some doesn’t but I believe that’s due to product line changes.
| GRiDCase 1500 Series Storage Backplanes | |||
| ID | Order PN | Labeled PN | Description |
| 00 | – | – | No FDD + No HDD (no backplane) |
| 10 | – | – | not exist |
| 20 | 104193-00 | 104194-00 Rev A2 | Dual 1.44 MB FDD’s (no HDD) |
| 30 | 104176-00 | 104177-00 Rev E | 1.44 MB FDD + JVC HDD (20 MB) |
| 40 | 105970-00 | ? | No FDD + IDE HDD |
| 50 | – | – | not exist |
| 60 | – | – | not exist |
| 70 | 104380-00 | 104381-00 Rev E | No FDD, IDE HDD (40/100 MB) |
| 80 | ? | ? | No FDD, JVC HDD (10 MB) |
| 90 | 104941-00 | 104942-00 Rev B | 1.44 MB FDD + IDE HDD (20/40 MB) |
| orange text is speculative | |||
Backplane Schematics (use at your own risk)
GridCase-1520-1530_Backplane-Type90_schematic.pdf
How Backplane Identification Works
Most backplanes contains logic chips and a customized GAL chip that together perform decoding, buffering, and identification.. The backplane’s circuits and logic are hardwired in a way that when port 6F8h is read a unique ID will be returned in the high nibble. When the GAL chip decodes 6F8h it triggers a flip-flop and buffer to return the backplane ID as the high nibble and whatever was already on the data bus as the low nibble. The low nibble is probably identification from an expansion pod in the accessory bay, but I haven’t confirmed that.
- Read one byte from port 6F8h
mov dx, 0x6F8
in al, dx - Mask to high nibble
and al, 0xF0 - AL contains the Backplane ID
Backplanes for floppy and IDE drives are relatively simple. They just contains basic off the shelf logic chips required for those functions and a custom programmed GAL chip that handles decoding. In most cases the backplane also passes power from the mainboard to the drives.
Backplanes for systems with JVC interface hard drives require and additional board that plugs directly in to a special place on the mainboard to support the hard drive.
JVC Controller Daughter Boards and Hard Drives
- 104140-00 10MB JVC HDD Controller
- 104141-00 20MB JVC HDD Controller 2A, 2B
- HD-JD3812 10MB JVC Hard Drive
- HD-JD3824 20MB JVC Hard Drive