Specifications
- CPU: Intel 8088-1 running at 4.77MHz (Standard), 7.16Mhz (Turbo), or 9.54MHz (Double)
- Optional 8087 math co-processor
- RAM: 640KB
- ROM: 32KB Phoenix Self-configuring BIOS (Versions 4.35 through 4.41 are known to exist)
- Chipset: Faraday FE2010A single chip controller IC
- Clock: Battery-backed Real Time Clock (RTC) maintains the date and time while the system is powered off
- Floppy Drive: One or Two 360K 5.25-inch (720K 3.5-inch optional on PC20-III) (SMC FDC9268 controller)
- Hard Drive: 20MB XTA (8-bit IDE) (standard on PC20-III)
- Sound: On-board piezoelectric beeper
- Ports:
- 9-pin d-sub Bus Mouse port compatible with Commodore Amiga 1352 mouse (MOS 5720)
- 25-pin d-sub RS-232 serial port (Western Digital WD8250-PL)
- 25-pin d-sub 8-bit Centronics parallel port (Paradise PPC1)
- Din-5 IBM PC XT-compatible keyboard port
- 9-pin d-sub RGBI/Monochrome video port
- RCA composite video port
- 9-pin d-sub Bus Mouse port compatible with Commodore Amiga 1352 mouse (MOS 5720)
- Video: Onboard Paradise PVC4
- MDA Monochrome Text
- Hercules Monochrome Graphics
- CGA Color Text and Graphics
- Plantronics Colorplus Graphics
- Alpha132 Monochrome Text
- MDA Monochrome Text
- 3 8-bit ISA slots for expansion
- 75 watt power supply
The Commodore PC10-III, PC20-III and Colt are IBM PC XT-compatible computers released by Commodore Business Machines in 1988. All three systems share the same motherboard with the main differences being disk capacity and minor cosmetic variations. Stickers on the motherboard and the back of the case sometimes identify these models as "10c".
The majority of the major ICs and the hard drives used in these machines were manufactured by Western Digital, or its subsidiaries Paradise and Faraday. Further, the low level format routine which can be called from DEBUG in DOS identifies itself as being copyright Western Digital.
Configuration and Upgrading
Processor
Processor Speed
Once the system has booted into DOS the following key combinations will change the CPU speed on-the-fly:
- CTRL+ALT+S switches the CPU to the "Standard" 4.77MHz speed
- CTRL+ALT+T switches the CPU to the "Turbo" 7.16MHz speed
- CTRL+ALT+D switches the CPU to the "Double" 9.54MHz speed
Processor Upgrade
V20 CPU Upgrade
If you choose to add a V20 CPU to your system, make sure that you use a V20 chip with the "-10" suffix in its model number. This denotes a 10MHz-capable part. If you install a "-5" or "-8" version, your system will be limited to 4.77MHz "Standard" or 7.16MHz "Turbo" and will behave erratically if you attempt to run in 9.54MHz "Double" mode.
To install a V20 CPU, simply lift the original CPU from its socket and replace it with the V20. No software is required.
286 Accelerator
Co-processor
To install an 8087 math co-processor, simply insert the chip into the empty 8087 socket on the motherboard.
RAM
Hard Drives
It is possible to add a hard drive to the PC10-III and Colt or to replace the hard drive in the PC20-III. There are two ways to add or replace a hard drive in these systems. You can either use the built-in XTA interface or use an add-in controller card. Using the on-board interface frees an ISA slot for additional expansion. Using an add-on card allows for significantly more models of hard drive to be used, and even multiple drives.
Built-In XTA Interface
Further, the first BIOS revision (4.35) appears to be limited to drives under 20MB. If you use a drive larger than 20MB on an early BIOS, the system will see it as a 10MB drive. With the ST-351A/X, it is possible to set a jumper on the drive to force it into 20MB mode. While this has the unfortunate effect of cutting the drive's capacity in half, it's better than leaving it at the default settings and only getting 10MB. BIOS version 4.36 and above are able to see the ST-351A/X's full size.
XTA compatible hard drives include:
- Western Digital 93024, 93028, 93034, 93044, 93048 (20-40MB) (95xxx variants are the same as the 93xxxs, but mounted in 5.25" adapters) - VERY UNRELIABLE
- Conner CP-2024XT (21MB)
- Seagate ST-351A/X (43MB) (Can be jumpered for either AT or XT mode)
- Seagate ST-325X (21MB)
- Miniscribe 8450XT (42MB)
Of these models, the ST-325X and ST-351A/X are probably the best choices. The ST-325X is ideal for machines with early BIOS chips. The ST-351A/X can give greater capacity in later systems, or be jumpered to 20mb for early machines. They are both quiet running and reliable. The Western Digital models should be avoided, despite being used in the 20-III from the factory, as they are highly unreliable.
To install a hard drive on the internal IDE interface, it must be enabled by a jumper. PC 20-IIIs with factory hard drives should already have this jumper in the correct position. Other models will likely need the jumper moved. The jumper in question is located directly beside the floppy interface and marked JMP208. To enable the on-board interface, it must jump the two pins which are in line with the other jumper block beside it. To disable the onboard interface and allow the use of an ISA hard drive controller, it must be moved to jump the center and outer pin.
Once a single compatible hard drive has been attached and the internal bus enabled, the drive will need to be set up with the built-in low level format tool. Observe upon booting the computer that the "Hard disk not found" message on the BIOS screen should have disappeared. If it remains, there is a problem with the drive or the way it has been attached. Confirm the jumper settings and the ribbon cable orientation. If the message is gone, proceed to the formatting stage.
From MS-DOS, run DEBUG.EXE. At the - prompt type G=FA00:5 and press enter. You should now see the Western Digital IDE Superbios screen, which you can use to configure the hard drive. Press Enter to select the first hard drive, enter again to accept the interleave value, then choose if you will manually enter the drive parameters or not by select Y or N for dynamically configuring. Some drives will need manual values entered, while others will be automatically detected. If you are unsure, try selecting N the first time and allowing it to automatically set up the drive. At this point the program will ask you to press Y to begin format. If the drive is working and properly configured, the drive should now be configured and low level formatted.
Once the system has rebooted, you may proceed to use FDISK and the DOS FORMAT commands to set the drive up as you would any other. Be aware that if you are using the factory MS-DOS 3.2 or similar, you will not be able to create a single partition larger than 32MB. Also be aware that you may need to instruct FDISK to make your primary partition active after you create it. If the partition has not been made active, it will not be bootable, though DOS will still be able to interact with it.
Add-In Controller Card
- MFM/RLL controllers are old, slow, low-capacity and unreliable
- ESDI controllers are old, still-kind-of-slow, low-capacity and unreliable
- SCSI controllers for 8-bit ISA are hard to find and expensive these days but will let you use most SCSI hard drives. The Seagate SCSI controllers ST01 and ST02 require BIOS 4.36 through 4.41 to work.
- The XT IDE Project here is an affordable way to get a lot of storage for very little money by allowing the use of standard 16-bit ATA/IDE drives in an XT system.
When using any add-in card, you must make sure that the built-in XTA controller is disabled. This is done with jumper JMP208 on the motherboard. To disable the built-in XTA controller, set JMP208 so that pins 1-2 are bridged. JMP208 can be found right next to the connector where the floppy drive cable plugs into the motherboard.
Floppy Drives
The floppy ribbon cable used in these machines lacks the twist between the end and the middle connector which modern PCs use to tell the drives apart. Instead, jumpers on the drives themselves are altered so that they may operate independently of each other. Drive A is set to DS0, while Drive B is set to DS1. Some early drives refer to the settings as DS1 and DS2, which can cause confusion. And not all drives will have selection jumpers visible on the outside.
Mouse
Keyboard
Operation and Software
The included operations manual has Commodore part #319964-02. The dealers service manual is part #314860-01.
Bundled Software
SPEED.EXE Utility
- SPEED.EXE -s switches the CPU to the "Standard" 4.77MHz speed
- SPEED.EXE -t switches the CPU to the "Turbo" 7.16MHz speed
- SPEED.EXE -d switches the CPU to the "Double" 9.54MHz speed
It is common to put "SPEED.EXE -d" in your AUTOEXEC.BAT file to set the CPU to its fastest speed immediately after booting.
SETCLOCK.EXE Utility
The SETCLOCK.EXE utility can be used to set the system clock by reading the date and time from the RTC or it can be used to take the current date and time from the system clock and write it to the RTC as follows:
- SETCLOCK.EXE -r reads the current time and date from the RTC and sets the system clock accordingly
- SETCLOCK.EXE -w writes the system clock's time and date to the RTC
These tools may be downloaded from the Software page, here.
ROM Tools
- G=FA00:5 loads the Western Digital IDE Superbios hard drive tool
- G=F000:0 loads COMMODORE 8088 Monitor
The PC10 has a 32kB BIOS EPROM that is split in three chunks. The first chunk is the first 16kb, 2nd is the following 8kB and the third chunk is the last 8kB. Each of them has an 8-bit checkum of 00. If reprogramming the ROM, be sure to correct the first, second, and third chunk's last byte. If you don't do this, the PC will not even begin to boot at all.
Video
- Switch 1 configures the character set - Up(Off) selects the USA/Europe Character Set and Down(On) selects the Scandinavian Character Set
- Switch 2 configures the adapter for monochrome or color output - Up(Off) selects monochrome output and Down(On) selects color output
- Switch 3 and 4 define the default video mode:
- Switch 3 Up(Off) and Switch 4 Up(Off) sets the default video mode to Monochrome
- Switch 3 Up(Off) and Switch 4 Down(On) sets the default video mode to 80 Column Color
- Switch 3 Down(On) and Switch 4 Up(Off) sets the default video mode to 40 Column Color
- Switch 3 Down(On) and Switch 4 Down(On) disables the on-board video adapter
Video Modes
CGA
- 80 column text mode (8x8 pixel character cell) in 16 colors
- 40 column text mode (8x8 pixel character cell) in 16 colors
- 320x200 graphics mode in 4 colors
- 640x200 graphics mode in monochrome (black & white)
These modes can be displayed as digital RGBI through the 9-pin monitor connector or composite NTSC video output. The display timings are:
- Vertical Frequency: 60Hz
- Horizontal Frequency: 15.7KHz
- Maximum Dot Clock: 14.318MHz
Plantronics ColorPlus
- 320x200 graphics mode in 16 colors
- 640x200 graphics mode in 4 colors
These modes can be displayed as digital RGBI through the 9-pin monitor connector or composite NTSC video output. The display timings are:
- Vertical Frequency: 60Hz
- Horizontal Frequency: 15.7KHz
- Maximum Dot Clock: 14.318MHz
MDA
- Vertical Frequency: 50Hz
- Horizontal Frequency: 18.432KHz
- Maximum Dot Clock: 16.257MHz
Hercules
- Vertical Frequency: 50Hz
- Horizontal Frequency: 18.432KHz
- Maximum Dot Clock: 16.257MHz
Alpha132
- Vertical Frequency: 48.7Hz
- Horizontal Frequency: 18.52KHz
- Maximum Dot Clock: 24.000MHz
Repair Info
Leaky Batteries
The machine can continue to operate without a clock battery so long as the user remembers to set the clock on boot. Replacement Ni-Cad batteries are available, as are sockets to install the more common lithium CR-2032 battery. In the latter case, however, it is vital that a Schottky diode or similar be installed between the battery socket and the motherboard, as otherwise the machine will attempt to charge the lithium cell with possibly explosive results.
Power Supply
The pinout is as follows, looking down on the motherboard:
- 1 Power Good (5V)
- 2 -12V
- 3 +12V
- 4 GROUND
- 5 GROUND
- 6 +5V