750 Family Device Support in Linux
Contents
Overview
The bad news is that the 750 is old and slow. The good news is that every device type in the family is supported in Linux. More bad news: Getting those device to work in Linux can be hard.
The 750 family has a few models. I will list their similarities first.
Architecture
CPU
The 750 uses an Intel 80486 running at 33MHz. Desktop CPUs now run 100 times faster. Some models run the CPU at 50MHz on a 25MHz clock. Linux requires an 80386 or better, so we are fine here.
Memory
The 750 came with 4MB memory built in and one IC DRAM card slot. It's like PCMCIA, and yet not enough like it to be useful. It has a 64-bit wide memory path that runs at 33MHz for a memory bandwidth of 267MB/s. It can accept a 32MB memory card. Linux will run with this small amount if you are careful.
Buses
The 750 uses the ISA bus. This means that the PCMCIA slots are 16-bit or PC Card slots. The memory runs at full CPU speed of 33MHz. The ISA bus runs at (unknown) MHz.
TrackPoint
The TrackPoint pointing device is supported perfectly in Linux as a PS/2 mouse.
Video
Controller
The video controller is the WD 90C24 and the 750 has 1MB video RAM. That's enough for 640x480 at 24 bits per pixel, or 1024x768 at 8 bits per pixel. It has been supported in Linux for some time. However, the chipset and video memory is not detected correctly, meaning hand-tuning of X configuration files is necessary.
Further, the svga driver (which includes this video chip) has not been ported to the most recent versions of X.org or X11R6.
Debian starts X with a display of 320x200 at 8 bpp. 640x480 with 4bpp should be easy and enough for the models without color screens.
There is a VGA connector on the 750 for connecting to an external monitor.
Display
Grayscale
- The 750 and 750P have a 9.5" STN LCD panel with 640x480 pixels. They can display 64 levels of gray and have a contrast ratio of 18:1.
Color
- The 750Cs has a 9.5" DSTN LCD panel with 640x480 pixels. It can display 256 colors and has a contrast ratio of 20:1.
Active Matrix Color
- The 750C has a 10.4" TFT LCD panel with 640x480 pixels. It can display 256 colors and has a contrast ratio of 100:1.
Audio
The 750 uses the Crystal Semiconductor CS4248-KL sound chip. That chip works with Linux in other machines. I have not seen it work on the 750. I believe that is because IBM puts the chip in IO address space that is not normally used in Linux.
The chip can reside at 0x0030, 0x4E30, 0x8E30 or 0xCE30. The last time I tried to pass in the address to the Linux sound driver, it didn't work.
PCMCIA
The 750 uses a PCMCIA controller that is well supported in Linux. Nothing special is required to get PC Cards working. Note that only 16-bit cards will work. 32-bit or CardBus cards will not fit in the slots without force and will not work if forced.
Power
The 750 uses Nickel Metal Hydride batteries. A fully charged battery in a 750 or 750P could last 12 hours. APM might work. Edit me.
Hard Disk
The 750 family came with either a 170MB or 340MB hard drive. Each drive was 17mm think and resided in a caddy that was difficult to disassemble.
The connector shorts pins 1 and 2 so that modern hard drives configure themselves to be the slave drive when they are plugged in. This stops most operating systems from installing correctly. To get newer drives to work, you can either bend or break the pin on the drive. Since laptop drives are usually the only drive in a system, this may not be as bad as it sounds. Instead, you can scrape a trace on the connector in the caddy or on the system board. This means that the older drives will no longer work in the machine.
Floppy Drive
The 750 came with a 2.88MB floppy drive. HD diskettes are hard to find nowadays. The floppy works with Linux, but the drive's diskette change status bit is reversed. Compensate for this by adding "floppy=thinkpad" to the kernel parameters at boot time, or the machine will not correctly recognize when the diskette has changed.
Ports
Linux supports the EPP parallel port fully.
The 16440-based serial port will also work but is a really awful device and may not keep up with modern serial devices.
The PS/2 port supports mice and keyboards with adaptors.
The 750 has no modem, infrared, or USB ports.
Esoteric Devices
A couple of devices were available to swap with the 2.88MB floppy drive.
TV Tuner
The 750C could use a TV tuner module. I doubt that video capture is possible with this device and that video was sent straight to the display, bypassing the video controller.
CDPD Modem
The 750 family (except the 750P) could use the CPDP Mobile Communications Module that allowed one to use old cell phone technology to connect to the telephone network. 14.4 kbps speeds were possible.
Differences
750
This is the standard, no-frills model. It shipped with IBM's PC-DOS 6.1.
750Cs
This model added a color screen. It was a dual-scan color screen, but still, Color!
750C
This model added a TFT color screen. It has similar specs to machines made twelve years later. At the time it was one of the best screens available.
750P
This model added an untethered pen. It could be used as a mouse or as an input device, like modern tablet PCs. This model shipped with PenDOS as well as Microsoft Windows 3.1 and Windows for Pen Computing, which included handwriting recognition and training software.
The 750P adds an internal 16550-based serial port to handle the pen's data stream. Linux does support input from tablets, but this device has yet to work on Linux.
750Ce
The 750Ce seems to be the step-child in the 750 family. It is not mentioned in the twbook specification book. From the Hardware Maintenance Manual, the CPU is an 80486DX2 running at 50MHz with a memory speed of 25MHz. It appears there was a 75MHz CPU option available as well. In addition, the TFT screen was "enhanced" in some way. Many parts are incompatible with other family members.
