CBM 500

As mentioned on the page for the B128, the CBM-II models were Commodore's last effort to capture the business market with it's superior proprietary technology. All the machines in this line are distinguished by the MOS 6509 processor, Commodore BASIC 4.0 (like that found in the later CBM/PET computers, the Commodore "SID" sound chip, IEEE-488 peripheral compatibility, an RS232-C port, and 80 column text video capability. Shown here is a early prototype 256k low profile CBM-II machine. This computer is part the "low profile" CBM-II series, called such because they feature a single integrated unit with a full business keyboard, numeric keypad, and 12 function keys. Being a 256k version of the 610, it stores 64K in bank 1 for BASIC code, and bank 2 for variables, but then adds banks 3 and 4 for variable storage as well.

The model number of this machine is hard an ascertain, though either CBM 500 would probably be most correct. The low serial number, CBM P500 back plate, West German construction, and top-mounted power supply point to its very early construction. This computer was initially constructed as a 128K machine. The second two banks of ram chips date from 1984, two years after the other chips. However, the CBM 700 EPROM chips inside are of typical Commodore factory make, and are mounted on typical Commodore factory make 28-24 pin adaptors. This suggests that the machine was upgraded by Commodore itself, and sold during the great CBM-II series dump of '84.

Just in case it is useful for identification, here is the assembly number of the motherboard and another marking. The number stamped in black reads "1983".

Statistics, features, and CBM 500 resources:

CPU: MOS 6509

• 2 mhz

RAM: 128 Kilobytes

• Expandable to 256k internal, 704k external

ROM: 24 Kilobytes

• 700 line Kernal (Download)
• CBM Basic 4.0 (View ROMs)
  • 256k Basic ROM Low(Download image)
  • 256k Basic ROM High(Download image)
• Character ROM(Download image)

Video: MOS 6545 CTRC

• Text: 80 columns, 25 rows.

Sound: MOS 6581 SID

• 3 voice stereo synthesizer/digital sound capabilities

Ports: CSG 6551/6525x2/6526

• Male edge-connector IEEE-488 port
• Male edge-connector CBM Datasette port
• Female RS232 port
• Round DIN CBM Monitor port
• Female edge-connector CBM-II/PET-II expansion port
• 1 RCA audio port
• Power and reset switches

Keyboard: Full-sized 102 key QWERTY

• 19 key numeric keypad!
• 4 direction cursor-pad

Resources

• 28 pin EPROM adaptor info
• CBM-II power supply information

Personal Note:The CBM-II line are personally very cool to me. I used to sit and write little BASIC programs on these things, but they fell out of favor as my collection grew, so now they are all boxed up. This machine, whatever its model, came from an eBay auction.

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