B500 & B500/B256

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 on the right is the 128k B500 computer, considered a prototype CBM-II model in the U.S. These machines are part of 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.

The B256 is the 256K version of the B128/B500. Whereas the B128 only utilizes the 64K in bank 1 for BASIC code, and bank 2 for variables, the B256 adds banks 3 and 4 for variable storage as well. Seen here is a factory produced B256 (256k) motherboard in a case whose sticker proclaims it as a B500 model machine. Whether any machines were actually released with a "B256" model number, or if all B256's are actually B500 model machines with 256k is unknown. This issue is further confused by the fact that the box this unit came in proclaims it to be a B256 proper, with no mention of "B500".

Statistics, features, and CBM B500/B256 resources:

CPU: MOS 6509

• 2 mhz

RAM: 128 Kilobytes

• Expandable to 256k internal, 704k external

ROM: 24 Kilobytes

• B500 line Kernal
  • (Download image)
• CBM Basic 4.0
  • 128k (B128) Basic ROM Low(Download image)
  • 128k (B128) Basic ROM High(Download image)
  • 256k (B256) Basic ROM Low(Download image)
  • 256k (B256) 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. The B500s both came from eBay auction.

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